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).
@adamralph commented (I see it in my e-mail, but can't find it in the review for some reason:

> Would it be fair to say that the laziness is an implementation detail? In which case the interface should have
> Lazy omitted but the concrete types should retain it.

I like this suggestion.