First stab at requesting image data back from the GFX backend.

This also changes |BitmapData.draw| to be synchronous since they must complete before image data is requested.
Merge branch 'master' of https://github.com/mozilla/shumway into avx
Disable HUD by default.
Fix AccessibilityProperties.
Merge pull request #1582 from mbebenita/avx

Avx