When using search in an option list, show matches in the list.

This commit is just a proof-of-concept, it needs more work to
be utf8-safe.

The function gtk_label_set_attributes() is also used to
unset attributes, by passing %NULL. Reflect that in the
argument annotations.

Factor out hit testing into a separate function.
This will be useful in the following commits.

Split GtkCombo up into GtkOptionButton and GtkOptionList. The
latter is just the list widget, which can be used standalone.
Add new tests in testoptionlist to demonstrate this.

Add a selection-mode property to GtkCombo, and implement
suitable behaviors. This requires the selected property
to change to an array, instead of a single ID. At the
same time change the terminology from 'active' to 'selected'.

This can be used to check for the presence of items as well.

Split out setting of sort keys and group keys from gtk_combo_add_item,
and rename the placeholder property to placeholder-text.

This fixes a cosmetic issue with those rows.

If we never unset separators, the stick around at the top of the
list during filtering.

Add documentation for GtkCombo.

Add a some simple test app for GtkCombo.

Add a new, simple combo box. The feature set of this is similar
to GtkComboBoxText, but it is using a popover and supports search.

https://raw.githubusercontent.com/gnome-design-team/gnome-mockups/master/theming/widgets/combobox-replacements.png

This way transient mouse movements over scrollbars don't cause flickering,
and more spaced movements have it enabled shortly.

Only horizontal coordinates are checked for the vertical scrollbar, and
vice versa.

This is so we can detect crossing events on the scrolledwindow widget,
which can be useful for toggling certain behaviors or not depending on
whether the mouse is on the widget.

On mice, scrollbars are always triggered temporarily. On proximity to an
scrollbar, it will be switched to full-width.

If the first of the month was falling on a Sunday, we would not
render any days of the previous month, and instead show two weeks
of the next month at the bottom. Improve this by showing one week
of each.

https://bugzilla.gnome.org/show_bug.cgi?id=301835

When changing between months, we can get into a situation like
'February 30", which GDate doesn't accept. Don't crash in that
case.

Changing font size does not cause widgets to update their size
properly anymore, since we forgot an invalidation flag. The
problem can be observed e.g. by running gtk3-demo and calling

gsettings set org.gnome.desktop.interface font-name "Cantarell 22"

The days that are not in the current month used to be rendered
in a ligher color. This was lost at some point. Bring it back.

Instead of old copy-paste code, use GDateTime to determine week
numbers and days of week.

On the wayland backend, set up GDK_WINDOW_SUBSURFACE windows
for popovers. In the popover code, the popover-relative-to-parent
calculation had to be tweaked, and it's been made to always prefer
the given popover position, since there's no sizing limitations.

https://bugzilla.gnome.org/show_bug.cgi?id=738891

gtk_builder_add_from_string takes more than 2 parameters.

https://bugzilla.gnome.org/show_bug.cgi?id=741897

The WM already adds the window shadow in that case, so just use the
box-shadow to add the border here.

https://bugzilla.gnome.org/show_bug.cgi?id=477454

We were asserting priv->filename != NULL in various places,
which leads to apps refusing to work when HOME is set to a
nonexisting or nonwritable value. Since it isn't hard, just
make GtkRecentManager survive without a filename. We won't
save or read any recently used files in this state, but
thats ok.
https://bugzilla.gnome.org/show_bug.cgi?id=739038

Provide a mechanism for hiding the "Quit", "About" and "Preferences"
menu items from the normal places in a traditional menubar layout (in
the File and Edit menus) when the menu is being rendered in the Mac OS
menubar.

These items can already be found in the application menu.

With this feature, applications can now define a single menu to use in
all 'traditional' scenarios.

Use this new attribute in Bloatpad.

https://bugzilla.gnome.org/show_bug.cgi?id=741610