Add new now playing widget mode

In an attempt to satisfy many users, I have added another mode to the
now playing widget. This shows the large cover art however it draws the song details
below the artwork, without the gradient that everyone seems to have a problem with.
This is just an option and all the original functionality is unchanged.
Add placeholder text for safety

Just to make sure that details_ has the correct height when initializing
Change height on details change

When the details change, the height is updated so if the details
now span more or fewer lines we can accompany that
Merge pull request #4347 from TheUbuntuGuy/master

Add new now playing widget mode.  Fixes #853