Effects menu

[itsrachelfish]

Currently it's possible to add "effects" to objects simply by using the custom classes input. This interface is not user friendly because it requires the user to know what all of the available classes are. It also prevents most effects (blur / greyscale / hue rotate / etc) from being applied simultaneously, since the classes override each other.

There should be a better interface for adding effects and the code should also be updated to allow multiple effects simultaneously.