Only reason to offload icon loading to background thread is to avoid
supposed network on main thread calls which happen only in debug since
icons are passed loaded from localhost.

* 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

This reverts commit abdb6e90a0.

* setTabButton -> has now the property 'label' to change the label of the TabButton

* Add to documentation

* [BugFix] use i instead of 0 to check all TabItems

* setStyle -> to change bottomTabBar

* update android

* remove hass...-functions

* update iOS set TabStyle

* iOS change icon color on buttonTabColor has been changed

* iOS update style-update rutine to update each viewcontroller in a NavigationViewController
tabButtonColor improvement

* iOS add forgotten header declaration

* iOS fix c&p error

* [Android] initialize colors for an empty AppStyles-Object

* [Android] fix update style of tabbar on display screen

* [Android] revert eventbus changes
[Android] apply guyca's solution

* [Android] rn 50 compatibility

* remove comment

* Support launch storyboards as splash screens

* default options support
* refactored navigation options

Application class can now be accessed statically using Context to access AppModule
which provides dependencies needed throughout the app.

Related to #2485 #2302 #1851 #1583

* Deleted getContentView method
* Delete Custom dialog code
* Delete topTab code
* sendOnNavigationButtonPressed was pulled to a dedicated interface

* Ensure ReactView isn't created after it's destroyed

Fixes #2490

* Rebase fixes and renames

https://github.com/wix/react-native-navigation/issues/1397

* readme

* doc

* topbar fix

* rm doc

* options presenter fix

* rm userless stuff

* WIP

* WIP

* WIP

* translation

* WIP

* todo

* draw under

* fix merge

* merge fix

* more merge fix

* improve calc

* animation improvement

* fix tests

* refactor

* refctor

* tests

* fix test

* anim improve

* rm outdated

* refactoring

* more refactoring

* tests

* refactor

* hotfix

* more refactoring

* refactor

* some more refactoring

* refactor

* Collapse topbar

closes #2487