Corbicula anti virus: Consistency

I contacted lluis about protected virtual issue with Stetic, he explained to me, that making event handler protected virtual didn't have any technical merits, rather practical. When an event handler is made private, mcs complains unused private methods are declared, but in reality they aren't unused, they're just dynamically bound by Glade/Stetic instead of assigned in the code itself. Making these methods protected removes these warnings. The virtual part isn't strictly nessecarry.

After understanding why event handlers are made protected by Stetic, I revisited the Corbicula codebase and made all my private and public (yuck) event handlers protected.