Refresh/Reload Canvas

[Tim Buchholz]

Describe your Issue

Canvas should be reloadable.

[Tim Buchholz]

To add to this:

Reloading does not clear the Vuex-Store anymore. But the Canvas will be empty.
If the canvas is set up the first time, it should ask the backend, if data is present.

If data should be present, the canvas can be set up one time by calling loadFromJSON http://fabricjs.com/docs/fabric.Canvas.html#loadFromJSON