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

closes #21

closes #312

This is needed since some of the data we need to send in the events
can not be serialised and added to a Bundle.

* Created Snakbar class to encapsulate Snackbar logic.
* Clicking the action now emits event to current screen
* Action color works

This commit closes #224 and fixes #252. Calling `setButtons` with
`leftButton` object still works for now but is deprecated and will be
removed in future version.

This commit adds support for displaying an activity with no animation
by setting `animationType: none` when calling `startApp`. In the future
we can support more animation types if there's a demand for it.