Piskel website adaptations :

M CanvasRenderer : can set the color used to represent transparency
M app.js : modified code responsible for saving when in website mode
M PiskelController.js : just some argument renaming
Cleanup of saving/loading process
PR138#commitcomment-4293036 use full namespace when specifying a classtype

See https://github.com/juliandescottes/piskel/pull/138#commitcomment-4293036
Merge pull request #138 from juliandescottes/piskel-website-adaptations

Piskel website adaptations