Boot ani: Allow background color to be specified

An RGB value may be added to the end of the first line
to specify a color to be used as the background instead
of black.  Black is the default when no color is
specified.

PS2:
Preserve custom background color when scaling animation
in ThemeManagerService.

Change-Id: Icf242a584513cfe974ef42f21f37a5d10400518b