* Change topBar backgroundColor to Color object
* StackLayout implementation
Unfortunately, this commit also contains a lot of refactoring and a few
bug fixes relating to styles.
* TopBar is not part of Component, instead it's a part of StackLayout
and shared between all components pushed to the stack Similar to iOS.
* Handle ScrollEvent in ReactView instead of passing the listener down
* Implement Fraction and Text null objects for style params
* Converted a few style params to null objects. This fixes some styles
being applied even when they were not specified explicitly.
* Stop sending null promise to commands
* Seperate push and pop into animatePush/push and animatePop/pop
to avoid boolean param
* Adapt TopTabs to new API
Guy Carmeli
Roman Kozlov
Guy Carmeli