This commit introduces an option to control the way components are pushed into the stack.
When pushing components into a stack, they are pushed the moment they are measured.
If `waitForRender` is true, components will be pushed only after the initial render.

api:

```js
options: {
  animations: {
    push: {
      waitForRender: true
    },
    showModal: {
      waitForRender: true
    }
  }
}
```

Unmount react views when bundle load completes

Users providing their own ReactNativeHost implementations should implement BundleDownloadListenerProvider
and make sure they set DevBundleDownloadListener when ReactInstanceManager.

* Set default statusBarBackgroundColor to Black
* Component and Parent controllers now extend ChildController
* Implement return to front logic for ChildControllers
* Apply statusBar color when view appears and returns to front

[Breaking[ Modal refactor

* [Breaking] Showing modal removes the previously visible ViewController from hierarchy
* Modal implementation does not rely on Dialog
* Modal view is added to `content` layout
* Overlay is added to `root` layout, on top of the application's content
* Introduce StackControllerBuilder
* Show modal with animation
* Dismiss modal with animation
* Add previous modal at index 0
* Add root at index 0
* dismissAllModals dismisses only top modal with animation

* External Component implementation

* Limit External component e2e to Android for now

* Reorder dependencies

Keep vs code happy

* Make markdown files readable on MacDown

* BackHandler compatibility

Give precedence to react's BackHandler when hardware back button is pressed

* f

* Update test

* Restore deps