Temp commit
Fix : frame and layer should be correctly selected when loading a snapshot state
Refactored piskel controller to extract the event creation
Removed cached serializer in Frame.js
Fix : layer manager was broken
Simplified SAVE STATE events, added wrap method to easily build decorators
Feature : undo redo including frame/layer actions

- Frame and Layer CRUD actions are now registered and can be cancelled
- Limited performance impact while drawing
- Improved frame cache invalidation
Enhancement : Selection tools various enhancements

- can use BACKSPACE key to delete selection content
  when no selection, backspace retains the default behavior
- cursor for rectangle selection has been changed to crosshair
- fixed a bug where selection seemed to be cropped when released out of
  the visible canvas
Merge pull request #168 from juliandescottes/feature-undo-redo

Feature undo redo