onInflate() onInflate() crash

[ghost]

We have an exciting family of crashes where:

• view inflation starts and lots of views are inflated, their presenters' takeView
  and onLoad methods are called
• Android senses a configuration change and never attaches those views
  • so their onDetachedFromWindow methods are not called
  • so their Presenters' dropView methods are not called
• the outgoing activity does call dropView for its own presenters
• A new activity starts, finds the existing activity scope and calls its onCreate method,
  before it calls takeView on its own presenters
  • it tells previously registered bundlers to onLoad
  • some of them are in presenters that still have views from the old config, so
    they go ahead and call presenter onLoad

So now we have child presenters trying to load, and possibly asking their ancestor presenters to do stuff while the ancestors' views are still null. Crashes ensue.

@dnkoutso and I are pretty certain that the fix is simple: make presenters debounce their onLoad calls. It's already the case that Presenter#onLoad will not be called until takeView has been received. We should go further and make certain that onLoad will be called exactly once for any View instance.

We haven't thought yet of anything that this will break, and can think of lots of things that it will fix.

[ghost]

PR forthcoming

[LukeStClair]

This also has the beneficial effect of making it much easier to work with observables - I was getting double subscribes in onLoad, which was quite surprising and leads to interesting side effects.