Provide public API for creating custom effects

There isn't currently a public API for creating custom Effect subclasses. Additionally, the concrete implementations of the existing effects appear to be closed source under com.sun.scenario.effect.*. This is a request for exposing a public API that end-users can utilize for creating their own Effects. This in itself would already be quite useful, but it will be even more exciting if/when JavaFX gains a public 3d API, assuming it could be leveraged within said public Effect API.