SkAR Java: refactoring main app class & finger painting class

Main things to look at:
1) onDrawFrame changes + moving many functions as separate helpers
2) SkARFingerPainting changes (name should change too)

Bug: skia:
Change-Id: I5068ce6c416a2f5d6c6c389cd63d08d5350e83e6
Reviewed-on: https://skia-review.googlesource.com/143701
Reviewed-by: Mike Reed <reed@google.com>
17 files changed