Supported actions:

1. never - Never show this item as a button in an Action Bar.

2. always - Always show this item as a button in an Action Bar.
Use sparingly! If too many items are set to always show in the Action
Bar it can crowd the Action Bar and degrade the user experience on
devices with smaller screens. A good rule of thumb is to have no more
than 2 items set to always show at a time.

3. withText - When this item is in the action bar, always show it
with a text label even if it also has an icon specified.

4. ifRoom (default) - Show this item as a button in an Action Bar if
the system decides there is room for it.

* Use navBarButtonColor to tint Toolbar instead of buttonsTint

* Use navBarTextColor to tint Toolbar instead of titleColor

The "disabled" property of RightButtons was not handled.

* Due to race condition when showing modal, buttons were added to
previous Toolbar.

* Minor refactor, moved `updateStyles` from BaseReactActivity to
StyleHelper class since it's now also used by RnnModal

Minor refactor after merging #52.

Adds BottomTabActivity which replaces TabActivity
Adds a dependency on `com.aurelhubert:ahbottomnavigation:1.2.3`
Uses iOS tabsStyle, with additional parameter that allows toggling of whether to show the titles of inactive tabs

This commit also fixes issue where style was not cleared when changing
tabs, and when pushing or popping screens.

Navigation views such as ToolBar, StatusBar, NavigationBar can now be
customized through a static JSON defined in each screen component.

Styling options introduced in this commit:

 - ToolBar color
 - StatusBar color
 - NavigationBar color
 - Buttons tint color
 - Title color
 - Tab normal text color
 - Tab Selected text color
 - Selected tab inidicator color