make the user model username 'unique' so that we don't have to check if the username exists here
added a check for the username to be unique
small formatting changes, because i'm anal about that...
made the system message be full width in its own row
added some documentation for the save function, removed a TODO that needed the database to rollback if afterSave failed (done), added a setFlash on the session for the 'unique' rule in the validate function