Add ability to set a different "style" to a notification.

This will make the notification center attempt to use a different theme if available.
Add ability for an alternative notification style.

All notifications theme must be of the same size.
Rename class members to match actual theme object name
Add support for templates in notifications theme.

available keywords:
%TITLE%, %IMAGE%, %ORIGIN%, %DECRIPTION%, %EXTRA%, %PROGRESS_TEXT%, %PROGRESS% (value between 0-100)