* custom titleView support

* custom navBar and titleView support

* refactored transition animations

* unit test fix

Otherwise, if the users sets custom insets (additional insets), they override the system adjusted insets. This is not the expected behavior.

* Update part of usage.md to reflect new API changes

* Update usage.md

It was handled inappropriately and some touch events were
intercepted unintentionally.

* adresses #1078

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

* Support creating stack with multiple children

* Add e2e

* Initial overlay implementation on Android

* Move logic to touch delegate

* Implement dismiss Overlay

* Overlay e2e

* fix iOS e2e

Currently the default NavigationReactNativeHost only adds the NavigationPackage. Users of React Native Navigation may need to override additional methods in ReactNativeHost. This change allows advanced users to provide their own implemenation of ReactNativeHost, with the requirement that they add the NavigationPackage themselves.

Closes #653

* overlay support

Only reason to offload icon loading to background thread is to avoid
supposed network on main thread calls which happen only in debug since
icons are passed loaded from localhost.