Add Text Area Size preference

This commits add the ability to set the size of the editable
text are for composing messages.

Arbitrary Restrictions:
Min Limit - 2
Max Limit - 15

Change-Id: I20261af0eb7e1daf80327df4cfde6b7efe766b1d

Conflicts:
	res/values/strings.xml
	src/com/android/mms/ui/MessagingPreferenceActivity.java