Deal with invalid recorded games

[schnapster]

There needs to be a way to deal with recorded games that turned out to be invalid.

As part of #78 some recorded games have been discovered that ended more than once. In that case, those with two recorded ending events are the invalid ones, but in other cases other rules might apply, so an automatic rule is hard to come up with. Rather they should be dealt with manually on a case-by-case basis.
Deleting them might be also be too destructive of an operation. I'd rather see them marked as invalid with a flag in the db, but that will also make any statistical queries rather complicated.