Rename gem update worker, add mailgun.

Rename gem update worker, add mailgun.
Add gem notifications.

Add gem notifications.
Add list gems to list.

Add list gems to list.
Add list gems.

Add list gems.
Add list parser.

Add list parser.
Add notifications.

Add notifications.
Add list update worker.

Add list update worker.
Remove implementation hint from gem update worker.

Remove implementation hint from gem update worker.
Add mail worker.

Add mail worker.
Add user fabricator.

Add user fabricator.