ListWidget.getValue now returns a list of proxies.

A call to listWidget.getValue().get(index) now returns a proxied
model (if the object is bindable), such that any bound widget will
be updated on change of state.
Fix for LessIntegration test.

Fixed race condition with GWT code generation, which caused test to
unpredictably fail.
Merge branch '2.4' of github.com:errai/errai into 2.4