Display Settings: Better font size control

Use a SeekBar instead of a list/spinner to determine the font scaling.
For consistency, an approximate size (small, normal, etc.)
 and the exact percentage are displayed.
Show a preview of the selected font size immediately

Ported from CM 10.2, squashed commits 46678 and 49167.
Credit to Veeti Paaananen for the latter commit.

Change-Id: I754d7fdcaf27c23dfccf9d56291956e70b23f63e
Merge remote-tracking branch 'upstream/cm-11.0' into HEAD

Conflicts:
	res/values/cm_strings.xml

Change-Id: I1f5c7e0c9b70e6df3820197e0f0f49e40bf104d2