Reward taggers/labelers

* Give points to people who tag other people, say, 1Dp per tag. In
order to avoid abuse, make each tag that is removed, cost the tagger
5dp. This will give an incentive (albeit a minor one) for people to
help categorise

* Give 2dp per mission tag. Allow some way for people to mark tags
as irrelevant (and punish if possible the same way as above) so as to
avoid abuse. It's generally a good idea to help with categorising
missions

* Provide a Badge for 100/200/400 tags that have not been deleted.