closes #454

Implement collapsing TopTabs on Android

specify `navBarHideOnScroll: true` in your `TopTabsScreen`

* Move event emmiter logic out of Application

* Implement searchView

Usage:
```js
rightButtons: [
      {
        id: 'searchView',
        label: 'Search',
        hint: 'Search...'
      }
    ]
```

* Translucent TitleBar

* Collapse TopBar

* Less noticeable translucent effect

* Implement ScrollViewDetector

* Collapse on fling

* Collapse on touch up

Complete collapse on touch up instead of fling

This commit removes necessary hacks which were introduced due to
limitations of previous React Native apis.

Mount/unmount logic isn't coupled to view attached/detached
to window callbacks. Instead, `unmountReactApplication` was added.
We can safely call it when a screen is popped and when application is
reloaded in debug.