* Adds iOS callback for viewWillAppear/didAppear e.t.c.

* Adds in screen events on Android

* Fixed issue with rightButtons getting ignored in preference for empty Screen buttons

* Android screen lifecycle

This commit is contains a few changes and enhancements to the PR made by simon:

* Use getEventEmitter instead of sendNavigatorEvent
* Dispatch willDisappear and didDisappear events when pushing screens
* Dispatch willAppear and didAppear events when popping screen

fixes #800 #797

* Fixed issue with rightButtons getting ignored in preference for empty Screen buttons

* Fixes setting transparency of navigation bar using setStyle or when no transitionCoordinator

* Set to use old bridge for compatibility with 0.30+

* Fixed crash occurring when tabBarBackgroundColor or tabBarButtonColor is not supplied

* Adds setStyle property to index.js

* Adds native code for setting style on RCCViewController

* Fixes setStyle function

* Fixes setting style on navigator

* Adds some styling to tab bar controller and fixes some bugs

* Adds ability to set modal presentation style

* Makes sure autoAdjustScrollViewInsets isn't propagated through when push another view controller

* Changes import to reference controllers rather than react-native-controllers and fixes setStyle mutating colours

* Fixed to work with RN 33

* Fixes updating title font styling with new RCCTitleViewHelper logic

* Fixes subtitle being shown

* Adds extendedLayoutIncludesOpaqueBars to navigation styling

* Adds ability to add shadows to text in navigation bar / tab bar

* Fixed merged ReactGateway.java file

* Fixed issue with rightButtons getting ignored in preference for empty Screen buttons

* Fixes compiler error

* added status bar color scheme for single screen which isn't pass on push. Set "statusBarTextColorSchemeSingleScreen" on the navigatorStyle

* make statusBarTextColorSchemeSingleScreen preferred option when both statusBarTextColorScheme and statusBarTextColorSchemeSingleScreen are exists

* To avoid white flash while component loads