Fix image import crash for first boot.
Fix for image become tall for some version of Android.
Ver 2.6
Update AndroidStuio.
Fix for transparent background cause stale brush cursor shown, scroll becomes black, etc.

Some code (overwritePaint related code) intend to fix brush top no inval problem, but nothing happen...
But this code is simpler, so I check-in anyway.
Ver 2.7.