AudioPlayer: convert headerbar into toolbar

Use a toolbar instead of a popup menu.
Turn the "Add to playlist" button into a menu item as well
and show an AlertDialog instead of a ContextMenu when pressing
on it.

When creating the "Add to playlist" dialog, do not add a
"New playlist" item by default and instead turn it into a
dialog action.

Change-Id: Ie54f49ba422ec0ef15f9437b3a74abfd56782e65
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>
Signed-off-by: Joey <joey@lineageos.org>