Added support for unloading moo

I recently found out that MooX::handlesVia breaks Moo's unimport code. namespace::clean and namespace::autoclean are not affected. I added a quick and dirty patch which solves the problem by overwriting the registered method in %Moo::MAKERS.

A cleaner way could be to provide a unimport method for HandlesVia, but I don't realy see a demand for this. I currently don't see any problems or sideeffects for my current fix.

If the fix is not included in HandlesVia, A statement in the docs which says that "no Moo" does not work if HandlesVia is in use would be nice.

I added some tests which ensure that namespace::clean, namespace::autoclean and not-cleaning-up-at-all work as expected. The only relevant test which illustrates my issue can be found in t/unimport/no_moo.t

cheers, lukast