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).
Thanks for info! (I forgot these two lines when splitting up the commits for the 2 PRs; the two arranged actions will be needed in the 2nd PR). Will be fixed.