Add machine management table and endpoint

Endpoints:
   * `/machines/`: `GET`, `POST`
   * `/machines/:hostname`: `GET`, `DELETE`, `PUT`

Table: `machines`
   * `id`: primary key
   * `hostname`: hostname, primary means to address the machine
   * `fqdn`: Fully-qualified domain name, used by IPMI to access the machine
   * `username`: IPMI username
   * `password`: IPMI password