improve performance of default puzzle tag population

[rawxfish]

Old code was doing a separate db query for each get_or_create on each default tag.

[rawxfish]

It's also called when you edit the hunt (it's sorta a hacky way to populate or de-populate the default tags)

[erwa]

Gotcha. Thanks for optimizing this!

[erwa]

oh, btw, did you find this performance issue after enabling silk in #656?

[rawxfish]

yes