Also changed the structure used to store Modals
from a Map based on navigatorId to a stack.
Reason for the change is that screens can be
pushed only to the topmost Modal.

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

From now on, calling start*Application will clear the activity stack and the new activity as
the root of an empty stack. This means we don't support "Modal" or opening screens in new activity.

Enabled resources (Toolbar icons) in release mode.

This bug caused app to start in white screen after it was relaunched since index file had already
run once.