Moved fake manager creation and initial configuration into the proxy generator (Part I)

This is the first part of PR #372 (we split it up into 2 PRs as mentioned there).

It solves #371 partially, namely that the default behavior is available inside the c'tor call. Therefore it also solves the bug #368 (see the `when_faking_a_class_which_calls_virtual_property_members_in_constructor` test case).
As you said, at the moment consumers should only access already constructed `FakeManager`s, so it shouldn't be a problem.

In the long term, we should think about extracting a new `IFakeManager` interface (with the minimal set of necessary methods), make `FakeManager` internal and just expose the interface (e.g. in `Fake.GetFakeManager()`). Should I create an issue?