Implement an object filter API

[beikov]

It would be awesome if we could implement an API that allows to filter a list of objects and their collections based on a filter predicate. I think that the Blaze-Expression language is restricted enough so that we can implement that in general.

I think that we will need to implement this by first translating the object graph to a tuple list so that we have a tuple per collection element, filter the tuple list by the predicate and finally try to filter the object graph based on the resulting tuple list. Maybe we don't need the tuple list translation step, but there are definitely challenges to solve for predicates that involve multiple collections like e.g. root.collection1.name = root.collection2.name.