We were not supporting plural form of the available space, which
is a problem in some languages.
However in this case is kind of a difficult matter, since we use a
formatted string from glib with g_format_size.

To fix it, use the same behavior as g_format_size to decide when
it should be used a plural form or not.

https://bugzilla.gnome.org/show_bug.cgi?id=759491

GtkPlacesView is a widget to display locations
in the computer, such as root ("/") and volumes,
separating the persistent devices from removable
ones.

From the latest mockups[1], GtkPlacesView would
display the available space of local drives like
partitions. This, however, is not implemented in
the current codebase.

Fix that by implementing the measurement of disk
space, and adding a new property GtkPlacesView::show-disk-usage
which controls the visibility of measured disks.

[1] https://raw.githubusercontent.com/gnome-design-team/gnome-mockups/master/nautilus/nautilus-next/other-locations.png

https://bugzilla.gnome.org/show_bug.cgi?id=759225

GTK+ is licensed under the terms of the GNU LGPL v2.1+.

When compiling inside GTK we also use the GTK_COMPILATION guard, as the
GtkPlacesView and GtkPlacesViewRow widgets are shared with Nautilus.

The current situation is somewhat sad, with the path
label totally misaligned throughout the rows.

This is fixed by using a size group for the path labels,
so they all have the same allocated size (with the max
of 15 chars). Also, instead of hiding the eject button,
set it child-invisible, so it is hidden and yet it's size
is allocated by GtkBox.

https://bugzilla.gnome.org/show_bug.cgi?id=757303

Otherwise, we end up using different metaphors in the place view
and in the sidebar, and nobody is going to know what the disconnect
icon means in this context.

http://bugzilla.gnome.org/show_bug.cgi?id=754022

P_() is meant only for property nicks and blurbs. Everything
else should use _().

Follow-up to 2d83dd62

http://bugzilla.gnome.org/show_bug.cgi?id=754086

Since we're dealing with networks, terms like "Eject" or
the eject button are misleading, since we're not actually
ejecting but disconnecting.

Fix that by showing the appropriate icon and tooltip.

It is needed to hook up the finalize method, since
it's overriden manually.

The GFile containing the Computer item was not
properly dereferenced, so plug that leak by both
dereferencing it and adding some reference management
on GtkPlacesViewRow.

GtkPlacesView widget manages persistent locations,
factoring out GtkPlacesSidebar functionality.

It, however, does not completely shows all sidebar
locations, since Computer is still missing.

Add a Computer item, adjusting some internal behavior
to make that possible.

Places sidebar shows XDG directories, mounted and unmounted devices,
connected networks, bookmarks and actions like 'Connect to server'
and 'Insert location', which causes the sidebar to grow very quickly
and look cluttered. Because of that, new mockups for the sidebar try
to simplify it.

To make the sidebar simpler, the new mockups propose that it should
only handle connected networks and removable devices such as flash
drives and USB devices, and delegates other devices for external
widgets through the 'Other Locations' item.

To handle fixed devices and manage network connections, add a new
widget named GtkPlacesView, based on Nautilus mockups to keep
consistency between GNOME file management tools - in this case,
between Nautilus and the bundled Gtk's file chooser.

https://bugzilla.gnome.org/show_bug.cgi?id=752034