2.0.0-RC1 Improve callability from Java code

[grote]

The 2.0.0-RC1 has some issues if called by Java code. E.g. instead of the FabSpeedDial.OnMenuItemClickListener, there now a strange Function3 that you can't really implement:

There's a similar issue for addOnStateChangeListener(). You can't just do

speedDial.addOnStateChangeListener(open -> {
	if (open) doSomething()
});

Because open is not a boolean, but <lambda parameter>.

Please ensure that the library can still be used with Java before releasing.