Merge pull request #1423 from tschneidereit/nat

AVM1 fixes
Match the apparent behavior of Flash when it comes to clipping masks that appear at the end of the display list.
Add option to disable clipping.
Don't overlap stage with the settings panel.
Adds a debugging canvas that can be inserted and removed via the release inspector option.
Merge branch 'nat' of https://github.com/mozilla/shumway into nat
Merge pull request #1424 from mbebenita/nat

Debbuging Canvas and Clipping Fixes
Enable execution of AS2 action blocks in nested MovieClips