Fixes ISSUE 307 Nav bar  showing on the nexus 7, 7 inch when the keyboard is shown

Fixes ISSUE 307 where the Nav bar was showing on the nexus 7, 7 inch
tablet in Portrait mode whenever the virtual keyboard was shown. 
The code changes also fixed another issue where the
orientationInitialized variable was never initialized to true causing
the initialization to be repeated everytime a handler was added. 

This code refactored the orientation handler into different files
initalized by GWT.create. This will enable other developers to implement
their own OrientationHandler if there is a bug in the current code.