[FEATURE] Monitor blockchain and record transactions in gatewayd (deposits)

Access to gatewayd in javascript is granted by passing the path to the gatewayd installation to the process environment, and using node to require gatewayd's database and config file access libraries.

    GATEWAYD_PATH=/path/to/gatewayd pm2 start deposits-manager.js

    #!/usr/local/bin/node
    const gatewayd = require(process.env.GATEWAYD_PATH)