view: don't hit tracker every time the user scrolls

Cache the number of items in the fully loaded view the first time
it's needed, and use that value for all future scrolling.

Note: if we ever support watching the library for changes, we need
to invalidate the cache.

https://bugzilla.gnome.org/show_bug.cgi?id=706025
Revert "view: don't hit tracker every time the user scrolls"

This reverts commit 7bf56d19ad0a54c2b8eb1f1591c216424db92cbc.

For some reason, the author was reassigned to me. Reverting this and
pushing a new one with the correct author field.
view: don't hit tracker every time the user scrolls

Cache the number of items in the fully loaded view the first time
it's needed, and use that value for all future scrolling.

Note: if we ever support watching the library for changes, we need
to invalidate the cache.

https://bugzilla.gnome.org/show_bug.cgi?id=706025
widgets: Cache vadjusment in AllArtistsAlbums.
Merge pull request #172 from JacksonIsaac/issue144

widgets: Cache vadjusment in AllArtistsAlbums
Added Slovenian translation
widget: remove call to '_on_scrollbar_visible'

Instead of calling this function. Call the _on_scrolled_win_change
function directly.
Merge pull request #176 from JacksonIsaac/fix114

widget: remove call to '_on_scrollbar_visible'
query: Sort albums by their title

The album variable in the query is redefined, so we should use the title
variable instead. Also, convert the title to lower case first before sorting.

https://bugzilla.gnome.org/show_bug.cgi?id=705093
query: Sort album tracks by their album disc number

https://bugzilla.gnome.org/show_bug.cgi?id=705038
query: Sort artist names case insensitively

https://bugzilla.gnome.org/show_bug.cgi?id=706242
Merge pull request #177 from gnome-prototypes-team/fix-item-order

Fix sorting of items
Add source file license notices

https://bugzilla.gnome.org/show_bug.cgi?id=700776
player: Has next and previous track should be false if there's no playlist

This prevents a crash when there is no selected playlist yet and an MPRIS
client tries to get properties of org.mpris.MediaPlayer2.Player interface.

https://bugzilla.gnome.org/show_bug.cgi?id=705855
Bump version to 3.9.90
Update README
Updated Polish translation
Updated Galician translations
Fixes for license notices

There are some missing words from the license notices, so added them in.
The non-GPL compatible GStreamer plugins exception is also added to the
license notices. Changed "Music" to "GNOME Music" in the license shown in
the About box.

https://bugzilla.gnome.org/show_bug.cgi?id=706457
Fix the upstream URL in the "about" dialog

This in fact fixes the URL in the configure.ac file, and then reuses
that in the "about" dialog.

If it needs to change in the future, then it can be changed only in one
place.

https://bugzilla.gnome.org/show_bug.cgi?id=706353