Simplify CopyProtoParticle2MCRelations

CopyProtoParticle2MCRelations nominally copies relation tables, but the copied tables are not actually used. The real reason it is executed is the side effect of the copying, namely the (optional!) cloning of the 'To' side of the tables. This MR changes the code so that it does exactly that cloning, and no more, so that there no redundant copies of the relation tables are made which are never used.

In addition, a few counters are added to improve the testing.

Must be applied in conjunction with Moore!3548 (merged)