Create a function that returns on roles: getRoles

[jaytula]

This requires the completion of #181 before starting.

The function signature should go something like this:

interface IRole {
  rid: number;
  name: string;
}

const getRoles => async () => {
  // return an array of role objects IRole[]
}

• This should go in db/roles.ts.
• Be sure to also write a basic test in test/roles.test.ts