Implement Open-Invitation Distribution

Lox should decide how to distribute open invitations. We have proposed handing out open invitations until they have been distributed to k(10) users and then moving on to another invitation. We likely will also need to decide an upper bound of buckets that can be distributed each day so that we don't run out of open invitation buckets. These are probably good enough for alpha and we should try to get metrics around how quickly we get to this k number of users each day as well as other things that can help us to refine this process.