indexed form panels

[David Durham]

I added index form panels to trunk. How it works:

new GXTFormBuilder(true).buildFormPanel(myFormConfig)

will return an instance of IndexedFormPanel.

IndexedFormPanel has 2 methods, getField(string) and
getFieldSet(String), though I have not yet added field sets to the
annotations. The basic idea is that for one off customization of
forms, it's pretty easy to autocreate the form panel, then go in and
access a particular field or fieldset for changes particular to a
form. Coming up with annotations for every customization scenario
doesn't make sense, and this approach is pragmatic.

I also added a demostration of this to the demo app, though this is
not deployed to appengine yet.

Please let me know if you find this feature useful. Also, please let
me know if you're actually using this library.

Thanks,

-Dave