Feat(#406): Allow filter[id] and filter[related.id]

[milosloub]

Closes #406

[milosloub]

@jaredcnance Concept of this is to register "id" as common attribute, work with this as user need (filter, sort....), but for output is ignored (to not double this property in top level and in attribute level).

My first try was to just expose id, but after that 5 tests were failing -> there are some quite hard dependencies. So I had to hide this and just change two Unit test that asks for attributes from
graph.GetContextEntity(typeof(TestResource));
Id is ignored in DocumentBuilder and those two test don't work with DocumentBuilder, so this is the reason to change Assert.Single to Assert.Contains

Btw - During this implementation I discovered, that DocumentBuilder.GetIncludedEntity() doesn't care about hiding null values as it's described in #454. But I let it be for now.

[jaredcnance]

Thanks! Looks good. One minor comment.

[jaredcnance]

should there be a continue here, after the id property is added?

[milosloub]

Yes, you're right. Now it's already there.