* Add support for react-native 0.52.0

* Refactore a bit

1. Rename `DevCommandsHandlerProxy` to `DevHelperProxy` so it reflects the changes in RN. See d19afc73f5 .
2. Add few comments to show which code is used on `RN >= 0.52` and which on `RN <= 0.51`.

* Now allowing the custom nav bar to take up the whole space on iOS

The custom nav bar on iOS was really just a custom view applied to the title of the navigation bar.
There were problems with this approach, because the navigation bar messes up the frame of the title very frequently, especially when the orientation is changing. That behaviour is accepted when the title is a label, but not when we have a custom component.

With this pull request the custom nav bar component can take up the full width of the navigation bar, no matter what orientation we're at.

* Added mix of native btns and custom component on the Custom TopBar screen of the example project

* Revert "Improve getCurrentlyVisibleScreenId on iOS with drawers. (#2052)"

This reverts commit 2c30a52bb9.

* Revert "introducing navbar shadow on iOS (#2339)"

This reverts commit 8fd496e0c9.

* Revert "This fixes an issue with a custom title-view (which has a title and a subtitle) appearing at the left side of the nav-bar instead of the center during a transition animation: when a screen with this title-view is being pushed or when you pop back to it. (#2384)"

This reverts commit 3f7f6c2612.

* Revert "Now allowing the custom nav bar to take up the whole space on iOS (#2306)"

This reverts commit 74a02ccfc5.

* Now allowing the custom nav bar to take up the whole space on iOS

- Also the custom nav bar reacts well to orientation changes
- Fixes: https://github.com/wix/react-native-navigation/issues/1893

* It now works well on iOS 11 as well

* v1.1.314 [ci skip]

* Added optional fixedWidth property to the Android side menu

    - Fixes: https://github.com/wix/react-native-navigation/issues/510

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