Add a close button to the Notifications popup to close it before the
default time.

Closes: #259

Use the default ones.

The selection-mode-allowed logic was used by DiscListBox to
distinguish the AlbumWidget use case (selection-mode allowed) from the
ArtistAlbumWidget one (selection-mode is not allowed).

Selection is now possible from an ArtistAlbumsWidget. Therefore, there
is no need for selection-mode-allowed.

It's not possible to select a whole artist from the ArtistsView
anymore. So, the selection-mode logic can be removed.

It is far more common to add individual songs than adding entire
artists.

It is always possible to select all songs of an artist with the Ctrl+a
shortcut (select all).

Closes: #26
Related: #146

GrlTrackerWrapper deals with differents models and "_model" is a
generic name. When reading the code, it is not easy to understand that
this model represents all the songs.

Rename it to "_songs_model" in order to avoid any confusion.

CoreModel deals with a lot of model and "_model" is a generic
name. When reading the code, it is not easy to understand that this
model represents all the songs.

Rename it to "_songs_model" in order to avoid any confusion.

It helps reduce the widget's minimum height.

Make sure that a non square album cover image is aligned with the list
of songs.

In the PlaylistsView, there is no vertical space between the bottom of
the Playlist and the bottom of the view. This makes it
harder to realize that the end of the list has been reached.

Fix the issue by adding some margin at the bottom of PlaylistsWidget.

This way, it matches the margin of the PlaylistsView.

In the ArtistsView, there is no vertical space between the bottom of
the ArtistAlbumsWidget and the bottom of the view. This makes it
harder to realize that the end of the list has been reached.

Fix the issue by adding some margin at the botom of
ArtistAlbumsWidget.

There is no need to be bidirectional. That way, another view will show
the correct song playing.

In the same logic as commit 0089ca26.
Validation property is a short-lived playability check for local
songs. There is no need to bind it.

This results in a wrong selection count because the same song is added
two times to the selected_items list of CoreSelection.

Besides, the songs of a playlist can not be selected. So, it is
pointless to bind this property.

Closes: #379

When last media is removed from the smart playlist (new_model_medias
is empty) the count property needs to be reset.

Closes: #376

On some setups (mostly flatpak), the first artist from the
ArtistsView's sidebar may not be selected on launch.
Indeed, it relies on listening to the artists-loaded signal from the
CoreModel to select the first artist once the artists model is
loaded. However, this signal may already have been emitted when the
ArtistView is built. In that case, the first artist will never be
selected.

Now, ArtistsView instead directly listens to the artists model for
changes and uses an initial state variable (untouched_list) to check
if it is needed to activate a row.

The artists-loaded signal from CoreModel is now unused. It can be
removed.

On some setups (mostly flatpak) selection-mode can be triggered on
launch when show_all is called in AlbumsView.
Indeed, if at least one AlbumCover has been loaded before the show_all
call, its check button will become visible. Because of a property
binding, this will change the AlbumCover selection-mode property to
True. This selection-mode change is then propagated up to the Window.

Fix the issue by removing the show_all call and making AlbumsView
visible by default.

Since fb9878fa starting to play a song from a new set player playlist
is relatively slow. It is however unneeded to bind validation back to
the main model song as it is just a short-lived playability check for
local songs.

Remove the validation property binding to remedy the slowness.

Since 41c60ec7 all the songs in the Playlist are matched to a songs
in the main songs model. The main songs model only contains songs from
the filtered location, so any songs in a playlist outside of this
location crashes Music as the hash match fails.

Add a location filter to the songs queries in Playlist to prevent this
from happening.

'pyexecdir' was used by JHBuild installations to find the associated
pygobject module. JHBuild is no longer used for development
purpose. Nowadays, flatpak is the preferred framework.

This can lead to some unexpected behaviors. See: #377.

The search path changes are only needed for `local-music` (i.e.: to
launch GNOME Music from the source tree).

Closes: #377

If a search is performed and allocation occurs and hides some results,
the 'visible' property of the widget in the FlowBox will be assigned
False. However, when a new search is performed, this property is not
updated to True, but the old value is kept. So, if the search results
for artist or albums happen to overlap with previously hidden results,
then last_child in _on_artist_flowbox_size_allocate() and
last_visible_child in _on_album_flowbox_size_allocate() can be None,
which will cause a crash.

To fix this, every time a new search is triggered all FlowBox widgets
set 'visible' to True.

Fixes #372

On rare occasions, the CoverStack can be destroyed while the art is
updated. This can result in an error once the art is retrieved because
the CoverStack does not have children anymore.

Since commit 2aa733b7, the SongsView
uses tabular number to display songs duration.

This is only possible since pango 1.44 because PangoAttribute needs to
be a boxed type (see
GNOME/pygobject#312)

By adding an explicit pango dependency, it prevents using Music
without the proper pango dependency.

Related: #374

On search Grilo would search online sources by default as well. This is
unwanted as it is a privacy issue.

Currently Music has no UI to enable/disable this by user request, go the
safe route and disable it for stable release.

Closes #317

Validation is only set in PlayerPlaylist, so having the property binding
one-way is fine.