Add stellar payments

- Adds core stellar payments library with client interface for adding payments to db.
- bundles mysql db layer

Relying upon the fact that `undefined == null` is IMO in poor form.  The nuance around == should be avoided, IMO, and you should just use `if(address)` instead.

Secondly, you should checking to ensure the address is a valid stellar address instead of just not null.  This isn't a blocker, but it should be improved, IMO.