Move all classes into one consistent place.

From dobedobedoh:

Andrew Lyons, [31.05.21 14:10]
Well core_antivitus is a subsystem, so anything related to antivirus as a subsytem should go there.

Andrew Lyons, [31.05.21 14:10]
core/antivirus is part of the core subsystem. Generally it shouldn't exist.

Andrew Lyons, [31.05.21 14:15]
That one should be relatively easy - move files, updates namespaces, and add to lib/db/renamedclasses.php. Find any other uses and fix those too.