This commit continues the work done in #2057.
When hardware back button is pressed, we handle it accordingly:

1. If screen was pushed with `overrideBackPress: true`, we emit `backPress` event
2. Let `BackHandler` handle the event
3. If the event wasn't handled by `BackHandler`, pop the stack
4. let the system handle the event

This reverts commit 3dd185ecad.

* animation fix

* fix tests

* hide toolbar

* default values

* default values

* tmp commit

* tests

* animated hide

* animated hode improve

* fix topbar

* readme

* lifecycle WIP

* lifecycle alert delay hack

* test fixes

* move topbar to container

* fix tests

* refactor

* refactor WIP

* refactor fix tests

* nav options fallback to parse

* WIP

* topbar background fix

Perform all stack related commands in performOnStack which
doesn't crash when requested stack is no found

* Add a button to the modal example to hide modal

* Render button only for iOS

Until now, buttons would use the same font family used by the title,
this commit introduces navBarButtonFontFamily property which allows to set
a different font family for title and buttons.

fixes #2038

* Support subtitle FontFamily on size on Android

Font family can be either a .ttf/.otf asset or one of the default font families:

* sans-serif (regular)
* sans-serif-light
* sans-serif-condensed
* sans-serif-thin
* sans-serif-medium

* update docs

While working I got a situation in which I wanted to open the side drawer on a button click. But I was not able to that. So I made some changes and now I am able to achieve the required functionality.

This prevented custom react views in navBar from being displayed if AppStyle was used.

* Fix style

* Fix resolving logic

* Fix styling

The only argument to `popTo` is the containerId to pop to, not the current containerId as well.  Also showing `this.props.previousContainerIds` lead me to believe that was included automatically (similar to `this.props.containerId`) so I changed that to avoid confusion.

The new path is `.../lib/ios` not just `/ios`

* animation fix

* fix tests

Since the docs suggested we remove everything inside the `didFinishLaunchingWithOptions`, without the return statement there was an `Control reaches end of non-void function` error since the function expects a boolean return. After adding this, the error goes away.

In the list of `LayoutTypes`, `tabs` is not defined, hence this throws an error. Replaced it with `bottomTabs`.

Fixes #1938 Closes #1900

This commit fixes two issues found in #1838. Fixes #1924
1. Keeps calling the deprecated reactInstanceManager methods when host is cleared
    to not introduce undesired behavior when clearHostOnActivityDestroy return true.
2. call onHostDestroy and onHostPause only if react context exists or is being created.

* remove unused code from tabStyle

* improve dummy screen ui

* set list screen translucent navigation bar

* make RCCToolBarView to composite the UIRootView inside

* add list screen for debug behaviours

* add dummy screen

* ui changes in ListScreen

* add push list screen function without add it to the button to the screen

* add and comment push list screen row

This only happens when you are using react-native@0.48.3, and your XCode is in version 9.0