Start app with the correct controls layout instead of showing the "hide elapsed time"
transition when started on mobile width. It is annoying.
We cannot detect surface width during app widgets assembly, so update the controls
revealers state on first surface update after window is mapped and only if running
on mobile width. Otherwise do not do anything like before which will result in
showing fully revealed controls (default).
Instead setting value to volume scale, set value to the player itself. Scale will be updated due to bidirectional binded property. This fixes cases where slider did not emit value-changed notify as it was being set to the same value as initial one.
Now that player API itself is operating on a cubic scale (no value conversion required), the volume slider can be bind to the volume property. Thanks to that, player volume scale will correctly reflect Clapper volume set via external applications e.g. gnome-settings.
The "clapper_src" directory name was unusual. This was done to make it work as a widget for other apps. Now that this functionality got removed it can be named simply "src" as recommended by guidelines.
