Improve DOM compatibility for Cordova support

-scripts can be loaded by appending script elements to document head
-getElementyByTagName can return these script elements
-add navigator object
-add document.readyState
-DOMContentLoaded is fired on window after tabris is started
-setTimeout works even before nativeBridge is present
-To support this, tabris.load can be used even after tabris has started, 
similar to $(function(){}) in jQuery and the deviceReady event in
Cordova.

Change-Id: Ie46808a913d628b12d27c50b5b982477c47636ae