WIP: Stopped the ViewPager consuming the pinch gesture.
WIP: Hook the pinch-zoom into the scrollview, allowing scrolling if pinch is not in progress.
Begin text scaling from default text size (rather than arbitary constant)
Add overflow menu items for larger/smaller text.
Save and load the text size in ShardPreferences
Registered fragment for SharedPreference change as fragments hidden by the ViewPager are still running.
Refactor: Tidy pinch-zoom code.