Return 200 for incomplete reimbursement errors

These do not need any further processing by wombat.  They will be picked up by the ninjas and processed manually. Thus, there's not much point to marking them as failed in Wombat.

It makes me a little nervous to return a 200 OK in a situation like this but from wombat's perspective there isn't anything further to do and the alternative of spamming wombat with extraneous failures seems worse.

Definitely open to other ideas if anyone has some.

Closes #27