Quantum cleanup: remove ToolkitInterface

com.sun.prism.render.* classes are of no value, just another level of abstraction that can be removed. RenderJob and Completionlistener can be moved to com.sun.javafx.tk, ToolkitInterface can be merged into Toolkit. In the short term we won't have other Toolkit implementations with different threading model, so they don't need RenderJob and CompletionListener, so the merge should not cause any problems.