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.
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