Fix missing import of PropTypes throwing an error on iOS

Docs weren't very clear on how exactly to return additional packages, i.e., as a <ReactPackages> list [Line 65]. 
Also changed MyApplication to MainApplication on line 54 (if that is a default and hasn't been changed by the developer).

Render children and pass props to children
Export SharedElementTransition on iOS
Omit children from passed props

Pass iconInsets for tab icon [iOS]

* Update app title (android)

* Add v2 docs placeholder path

Add payload param to handleDeepLink

also report type as ScreenChangedEvent instead of navBarButtonPress.
closes #1144

Custom title view in navigation bar support in `navBarComponentAlignment:'fill' | 'center`

Usage is identical to switchToTab, closes #842