Display Settings: Better font size control

Use a SeekBar instead of a list/spinner to determine the font scaling.
The minimum and maximum default font sizes have been preserved.
For consistency, an approximate size (small, normal, etc.) and the exact percentage are displayed.

Change-Id: I96f80d93e740a25a6a6890b423a41c3900b93767

Conflicts:
	res/values/attrs.xml
	src/com/android/settings/DisplaySettings.java