This commit applies the save props mechanism used when pushing screen
to navigator buttons as well, enabling us to pass unserializable props to buttons.

* throwing an error instead of a string

* return a callback to remove the register handler

Fix props loading from PropsRegistry in custom buttons

This reverts commit e69f3801b9.

This fix allows to pass unserializable props to custom buttons, such as navigator or functions.

fixes #2166

This commit adds ability to register multiple navigator event listeners:
navigator.addOnNavigatorEvent(func)
navigator.removeOnNavigatorEvent(func)

Event listeners are removed when the screen the navigator is bound to
is unmounted, calling `removeOnNavigatorEvent` isn't mandatory.

As this api conflicts with the current api, addOnNavigatorEvent can't be used
in a screen where setOnNavigatorEvent was used before.

On some devices, when returning to the app from background, some launchers
open the SplashActivity over the NavigationActivity. In this case, simply finish the SplashActivity
and return the the preview NavigationActivity.

This is potentially a breaking change as calling navigator.switchToTab()
won't do anything now if the current tab is already selected.

closes #2143

No major changes, just tweaked values a little bit.

* Fab animation duration changed to 120 (previously 200)
* Fab show animation: Scales from 0.6 to 1 (previously 0)
* Fab hide animation: Scales from 1 to 0.6 (previously 0)
* Removed alpha delay from screen animation
* TranslationY value changed from 8% to 5%

* Support showing modals with the default screen push/pop animation

* Set navigation bar color before modal is displayed

* Implement screenAnimationType property

controls animation type of all screens including modals.

added some elaborations to make it easier for developers with no ios experience.

Since status bar style was applied when the screen was created, this caused a noticeable
artifact in status bar color.

When toggleTabs was called, the visibility state of the BottomTabs
was not persisted. There for, when pushing a screen and popping
the BottomTabs visibility state was set to the value of bottomTabsHidden
from navigatorStyle.

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.

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