Migrated to Extjs4.2.1

I have migrated graphite to Extjs4.2.1 (dashboard still using extjs3).

You can test it with expanding a large tree(1000+ nodes), it's much musch faster, this is the reason why I migrate it.

I kept most of html, composer.js, composer_widget.js, completer.js...code in the composer_extjs4.js, composer_widget_extjs4.js, completer_extjs4.js files.

Since the api to create "tree" has changed in extjs4, I change the way to create new tree in browser.js, trees are created with treepanel in browser_extjs4.js.
The user graphs and my graphs become a new tab. (I don't find a way to use multiple stores in one tree panel, have to put them in new tabs)

I also included the basic extjs lib files under graphite/webapp/content/js/ext4 and ext-theme-classic.

The composer look and feel should be the same. I have done basic UI tests, let me know if you find any bugs.

Thank you.