Continued work on Android

* Rename TopTabsLayout to TopTabsViewPager
* Pass ScrollEventListener from component
* Change ViewController.view to protected
* Don't keep ref to view in ComponentController
* Pull IReactView and ReactViewCreator to separate classes
* Ensure ToolBar.menu is created before clearing menu items
* Unmount react view before destroy
* Let TopTabsController set mediator in view visibility handling