Update HWUI to store its own SkBitmap objects

This enables us to...

1) simplify the lifecycle/ownership between Java and HWUI
2) remove DisplayListRenderer::drawBitmapData and associated logic
3) track pixel lifecycle using standard SkPixelRef refcounting
4) Remove uncessary calls to ref/unref the bitmap's pixels and colorTable

Change-Id: I3c95078da20995444f6388a029414280fd654318