Upgraded ExtJS library to 4.2.1

- Upgraded ExtJS library to 4.2.1:
 - lib/extjs/src directory is complete-copy paste of Ext Js 4.2.1.883. Except 2 lines of code had to move in lib/extjs/src/Ext.js (see code comments)
 - Added stringdom dependency and created window, document and navigator globals to allow the Loader and EventManager
- Version bump to 4.2.1 (In sync with Ext JS version)
- Removed requirement for node version < 0.7.0