Wire up Glass EventLoop API to Quantum/FX

Glass introduces new API for handling nested event loops - the com.sun.glass.ui.EventLoop class and the Application.createEventLoop() method. This API allows for interleaved enter()/leave() method calls, and as such is more robust. Also, it is needed for Deploy to proceed with RT-16673. An example of using this new API can be found in the Rain demo in Glass repo (see Main.java - handleEventLoop() method).

This API together with its specification (see the EventLoop class) need to be wired up to FX.

Legacy methods Application.enterNestedEventLoop() and leaveNestedLoop() will be made private, and as such inaccessible from Quantum/FX once the new API is wired up.