* Renamed Selection data structure. Multiple select begins to work
* Saving and loading of multiple selection shapes implemented
* Renamed Document selection properties to avoid confusion
* Renamed and distributed functions between selection and shape utilities
* Fixes to selection toolbox
* Fixed issue with copying across multiple selections
* Final cleanups
* Selection outline is now rendered by interaction pane, not individual layer sprites
* Updated to zCanvas 4.3.1 to fix issue with bounding box detection on rotated content
* Refactored rectangles to always use left and top
* Layer scaling, rotating and mirroring is now a fast, synchronous operation
* Snapshots are now always of rendered layer content
