Roles

- Removes the `common` role. As discussed with @lyndsysimon and @JeffSpies , common server setup can be handled in a more explicit way using a playbook
- Replaces the old roles from `the-ansibles`, which have deprecated, with their newer counterparts on ansible-galaxy.
- Removes a few unused roles, including `logwatch` and `powerdns`. We may decide to use these in the future (esp. logwatch), but they don't need to be a part of common server setup for now.