implementation of a BindingsValuesProvider to inject QueryBuilder

Inspired by one of the sessions at Circuit Conf, I threw together this trivial BindingsValuesProvider which adds `queryBuilder` as a scripting variable.

NOTE - this, like BVPs in general, are of limited practical use in JSPs because of limitations of the JSP script engine (basically, the list of scripting variables can not be dynamic). In a JSP, you need to do something like this:

    QueryBuilder qb = (QueryBuilder) bindings.get("queryBuilder");

But in other scripting languages which don't have this limitation, this is a bit of syntatic sugar.