Changed playlist-menu-header styling.
Added playlist-info content to the page and made a basic styling for it.
Refined playlist-info styling.
Implemented playlist-info functionality.
Refined playlist-info styling.
Merge branch 'style-playlist-menu'

I modified the styling of the playlist-menu, and added a player-info box to it.
The player-info box is automatically updated whenever a playlist is activated or renamed,
or a record is added to or removed from the playlist.