Can be null if returning from another app and our activity wad destroyed in background

* [iOS] Added fade transition animation between screens

* Update docs for #1367

* Fix iOS drawer status control

* Prevent MMDrawerController disabling UI interaction when accidentally assigning a nil drawer controller and toggling that drawer

* setDrawerEnabled with params side and enabled

* Tweak docs, small RCCDrawerController fix

* Correct indents

* Correct indents

* Fix title bar not displayed if it was initially hidden

Also cleaned up VisibilityAnimator.

* Move visibility animator into topBar

This reverts commit 7919e65932.

Also cleaned up VisibilityAnimator.

* changed this.props.id to this.props.containerId

* fixed js tests

* refactor

* Fix disabledBackGesture.

This `return self._disableBackGesture ? self._disableBackGesture : YES;` check is incorrect, it's the same as `true ? true : true;`.
Also `_disableBackGesture` was never set. We should just `return disabledBackGestureBool` (bool value of the prop).

* [iOS] Enable back swipe gesture when a navBar is hidden. Resolves this issue: https://github.com/wix/react-native-navigation/issues/930

added 03d380f8a9 back and also applied this fix https://github.com/wix/react-native-navigation/issues/428#issuecomment-278268928 on top of it

* Revert accidental commit: 3cdb1b37f6

* Change "tabs" to "bottomTabs"

* Fix failing test