Started Sprites + Minor player fixes and regarding the editor 

Sprites basic code is: Mar 29 — Apr 2 commits ( 5e319ce...9b64a5c ] all other are fixes.

Changes:
* `Image` is a custom case of `Sheet` (with one frame taking all the picture)  + caching mechanics are changed, all images internal operations are simplified now because of it.
* Background color of the canvas is any RGBA color, a project may have even a gradient as background, and these two options are different (canvas background is applied all the time, scene background is drawn over it (if it was specified) while scene is loaded into player).
* Preview is now zero-frame by default.
* Checking if player is already attached to this canvas
* Handling `C.NOTHING` state for Controls and Info properly
* `embedding.html` page to test embedding with URL parameters for the editor
* Some internal drawing improvements