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.

Change-Id: I96f80d93e740a25a6a6890b423a41c3900b93767
Merge "Display Settings: Better font size control" into cm-10.2
Merge branch 'cm-10.2' of git://github.com/CyanogenMod/android_packages_apps_Settings into cm-10.2