Use custom BottomNavigation view.
change BottomTabActivity layout, content frame is now being drawn
behind BottomTabs.

When ever bundle was reloaded, all currently registered screens
where recreated since they were still attached to the react context.
This commit adds, in a very hacky way, means to respond to bundle
reload events.

Since Toolbar icons' height is set according to Toolbar height,
We need to ensure the call to `setupToolbar` from `onCreate` is
called after the Toolbar is measured.

* Due to race condition when showing modal, buttons were added to
previous Toolbar.

* Minor refactor, moved `updateStyles` from BaseReactActivity to
StyleHelper class since it's now also used by RnnModal

Toolbar buttons not updating
Pushes into BottomTabActivity not always working
Modal not closing properly when back pressed

Minor refactor after merging #52.

Removed propTypes from example-redux screens

Adds BottomTabActivity which replaces TabActivity
Adds a dependency on `com.aurelhubert:ahbottomnavigation:1.2.3`
Uses iOS tabsStyle, with additional parameter that allows toggling of whether to show the titles of inactive tabs