Style
Revert "Make Cocoa view sources non-generic"

This reverts commit d099607e659ea5be6df830303bb327919241070c. Starting with
Xamarin.iOS 7.2.1 you can use generics with NSObject
Not sure how this was missed
Merge remote-tracking branch 'origin/rxui6-master' into weak-references

Conflicts:
	ReactiveUI.Platforms/Cocoa/ReactiveCollectionViewSource.cs
Revert "Make IReactiveObjectExtensions internal."

This reverts commit b79c3a6b6acaa87bd04f8b64f5006f711df183d3.
Merge branch 'weak-references' of https://github.com/reactiveui/ReactiveUI into weak-references