[User Roles] Add a Read only role

[garyhtou]

We already have a manager and member role. Let's add a read only role.

The goal is that adding this goal is increase the number of teenagers on HCB. At the moment, we have a large number of FIRST robotics teams. But those organizations usually only have the coach (no teenagers). By adding this role, we can encourage coaches to add their team.

@manuthecoder, would you be interested in working on this?