This patch fixes the keyboard navigation in the library selection of the
main app bar. Without this patch, no options are selectable via keyboard
and selecting an option and hitting return has no effect.
This patch highlights items in the app bar if a user uses the keyboard
to navigate in audiobookshelf. This ensures that users actually know
which item they have selected.
This also modifies the text for the library selector, so that users
which are using a screen reader understand that it is a selector for
libraries and not only a button related to the current library.
