reusable sanitize method for gradient arrays

because we also need that in GradientGlowFilter
===
unit tests and implementation GradienGlowFilter
Beginings of layer blend modes.
Paint frame container bounds.
Factor out region allocation in its own file and add test case.
Merge branch 'nat' of https://github.com/mozilla/shumway into nat
Dispatch added & removed events
Dispatch render event only for display objects on the display list
Prototype layer blend modes.
Merge branch 'nat' of https://github.com/mozilla/shumway into nat
Fix setChildIndex
Fix addedToStage dispatching
Merge branch 'nat' of github.com:mozilla/shumway into nat
Cache Event instances
Some test cases.
Merge
Fix and optimize timeline events and inter-frame navigation
Small text related fixes
Save and restore current frame phase
Rename timeoutID
Faster grid allocator, added a bucket allocator based on the grid allocator, remote misc display object properties.