Draft: Created migration tool for moving events from sql to mongo

Added exporter which is a sort of playground, but it's currently setup to connect to both a mysql db and mongo and move events over. The biggest change is with how loadouts are encoded. An equipment lookup table for encoding/decoding was generated in the process. An ID is reserved whenever a new piece of gear is encountered.

Moved both SBI and DB models out of internal and into /pkg so that they can be shared with other murderledger repos.