Enable theming lockscreen wallpaper via ThemeManager [2/2].

PS2:
Adjust mixer item height to accomodate mutliple lines of text.
This requires setting the layout height in the adapter since
GridView is being a PITA and not honoring the height in the
layout.

PS3:
Use fixed dp size for mixer label.

Change-Id: I920765c15b4fc61ffecae5cbe0336bf9ab8205d8