Whoa! Fragments!

I've spent some time fixing up Fragments and ViewModel rehydrating and saved states. This is only done in the Fragging library, but should be easy enough to pull out and put into the FullFragging library.

I've made a small sample showing it working here: https://github.com/Cheesebaron/MvxFragmentsAndHamburger there is a small readme telling what it does and what to expect.

Could someone review this, probably not the cleanest code, but it seems to work!
I'd assign the result of _currentFragments.ContainsKey to avoid a double look up.