[FEATURE] submit memos & invoice_id to the ledger

Submit memos & invoice_id to the ledger from gatewayd's ripple_transactions record to rippled via ripple_rest
Can now use gatewayd.database to sync all tables:
```
beforeEach(function(done) {
    gatewayd.database.sync({force: true}).then(function() {
      done();
    });
```