Remove dependancies on Firebase from objectlib.Report such errors to the application via the Interface.
Progress with PuzzleTester app.
Major change: separate the notion of a TwistyObject and its Node. Now,
1) the Node stays when we change objects (this makes transitions faster)2) it's possible to just create an Object without adding it to the Screen (now app needs to explicitly create the Node and add it to its Screen itself)
Remove unneeded API.
Relax objectlib's requirements: it can be displayed not only on top of a DistortedScreen, but any DistortedFramebuffer.
Remove the concept of a 'TwistyActivity' altogether.