Implement Element transition on Android

This commit adds basic support for Element transition to Android.
Currently, only Shared Transition is supported and only when pushing screens.

There are a few caveats you need to be aware of if you intend to use
this feature in its current state:

1. Since elements need to be laid out before the transition can start, Set `waitForRender: true` when pushing the destination screen.
2. Fade animation has to be used when pushing screens with shared elements.

API

```js
options: {
  animations: {
    push: {
      waitForRender: true,
      content: {
        alpha: {
          from: 0,
          to: 1,
          duration: 250
        }
      }
    }
  },
  customTransition: {
    animations: [
    ]
  }
}
```

* Refactored bottomTab and bottomTabs

* Initial commit before switching to our fork of AHBottomNavigation

* Bump AHBottomNavigation version

* More work on BottomTab options

Need to merge some child options when a child is attached to parent

* Fix tests

* DefaultOptions refactor

* defaultOptions are now merged before applying options
* Handle BottomTab options in dedicated presenter
* Create BottomTabs in BottomTabsController.createView() instead of constructor

* Set bottomTab TypeFace

* Update Android installation guide

* fixed unit tests

* Fix unit tests

Kind of a workaround

* Handle NPE in getPreferredHeight

If a view hasn't been attached yet, return 0 height

* Apply BottomTab text and icon color individually

wix-playground/AHBottomNavigation does not support setting color for the entire tab (icon and text),
instead it supports setting color individually to text and icon. Another change is that it no longer supports
default color for icons. If icon color is undefined - it won't tint the icon.

* Add getCurrentChild to ParentController contract

* Clear backButton when setting stack root

* Add  ViewController.resolveCurrentOptions

resolveCurrentOptions merges the controllers options with all of its current children

* StackController refactor

* Create pushed child view only in StackController.createView
* When initialising a stack with multiple children, only create the top child's view
* StackController constructor now accepts children
* When pushing child to stack, apply options that change LayoutParams

* Apply BottomTabs layout options when tab views are created

* bototmTab changes in iOS

* options fix

* Fixes options propagating

* Support RN 0.55.4

This commit adds support for RN 0.55.4 by introducing version specific build flavors - reactNative51

* Update scripts after introducing build flavors

* Update Android installation instruction on specifying build flavor

* Upgrade Gradle version

* Allow playground app to run on x86_64 emulator

* #1071 Allow changing navigation title

* #1071 Add tests for JavaScript

Fixes #338