Correctly take account of padding when calculating the view size.

Always use whichever dimension is smaller as the final size.
Replace non-functional "Download" option menu item with a context menu.

The "Download" option menu item did nothing.  Remove it, and add a context
menu to now_playing_fragment_full.xml.  Add the Download menu item here.

As there's now an available context menu, use it to also show menu options
for viewing songs on the album, albums by the artist, and songs by the artist.
This replaces touching the track, album, and artist name views, which were
small touch targets.

Trying to fit the context menu in to the existing LinearLayout created many
nested views, so switch to using a RelativeLayout for
now_playing_fragment_full.xml.