Currently exporting `backButton` id, usage: `Navigation.constants.backButton`

Pass child ViewControllers in constructor and create tabs in constructor as well

Fixes #2996

* Update docs

Outdated onAppLaunched part is changed

I just started to a project with v2 and I realized this part of the documentation was wrong. I searched a bit and find this 2 commits: 

104e3f97fd

1d2680c5aa

So, that part is probably forgotten

* Modal unmount e2e test

* Modal unmount e2e test changes.

Fixes #3138.

AHBottomNavigation recreates all tabs when some style properties are set.
This commit works around this issue by setting the problematic style properties
only if they are different then current values.

Related to #3132

* Implementation of passing multiple arguments to ImageLoader in order to avoid asynchronous issues and for performance as BottomBar re-creates all views every time an item is added

* removed redundant checks for testId

* Implementation of passing multiple arguments to ImageLoader in order to avoid asynchronous issues and for performance as BottomBar re-creates all views every time an item is added

* removed redundant checks for testId

This prevents the call to mergeOptions from applying statusBar color even
though it was not declared explicitly by the user.

* Set default statusBarBackgroundColor to Black
* Component and Parent controllers now extend ChildController
* Implement return to front logic for ChildControllers
* Apply statusBar color when view appears and returns to front

Outdated onAppLaunched part is changed

I just started to a project with v2 and I realized this part of the documentation was wrong. I searched a bit and find this 2 commits: 

104e3f97fd

1d2680c5aa

So, that part is probably forgotten

Options.java was missing from previous commit

This commit removes NavigationOptionsListener as it was not needed anymore.
As a result, it uncovered a few issues which this commit also aims to fix.

* Set SideMenuController as parent of left, right and centre controllers
* Select tab by id with tabSelector interface
* mergeOptions now also applies options after merge - in ViewController base class
* Pull presentation logic from ComponentLayout to ComponentViewController

This commit also consolidates index files in the playground app

* Cover OverlayManager with unit tests
* Add e2e to test Overlay unmount

* Assign commandId to async commands

* CommandListener refactor

Pull listener out of Navigator and implement NativeCommandListener for native commands

* Emit onNavigationEvent when commands complete

* Rename timestamp to completionTime

* Rename NavigationEvent to EventEmitter

* Rename sendOnNavigationButtonPressed to emitOnNavigationButtonPressed

* Emit navigationEvent on bottom tab select

* rebase fix

* Emit commandCompleted event instead of nativeEvent

* fix native ios commands

* wait show and dismiss Overlay

Both events broke in 104e3f97