Allow overruling of annotated filters in request broker

[mikey]

The request broker should be enhanced in a way that allows to overrule the annotated filters with some kind of map, where the key is the name of the property/method to overrule and the value is an instance of net::stubbles::ipo::request::filter::stubFilter which will be used instead of the annotated filter.

[mikey]

Implemented with r1667. The key in the map is the fieldname, as this is most likely better known then the method or property of which the annotation should be overruled.