CORS + Tainted canvas w/r/t BBModBrushManager2D

[brannondorsey]

Loading images from other servers and using them with the BBModImageBrush2D class can cause BBModBrushManager2D's canvas to become tainted. For this reason the documentation for both of these classes should clearly document this. More here:
https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image

[brannondorsey]

It appears that Safari completely refuses to use any of our images (at least when served via MAMP) with error Cross-origin image load denied by Cross-Origin Resource Sharing policy.

[brannondorsey]

The NS_ERROR_NOT_AVAILABLE error in Firefox seems to be fixed by removing

this._fboImage.crossOrigin = "anonymous"

In the BBModBrushManager2D constructor. For now I am going to keep that line commented out as it fixes the brush manager functionality (at least some of it) for Firefox and Safari, but more research needs to be put into CORS + why setting crossOrigin = "anonymous" is causing this error.