Pathfinder/m4change - add user_data to locations

Added user data to locations, because it makes sense for our CCT site use case. The way we have it now lets two separate users assigned to the same location have different CCT status, and CCT should be enabled/disabled per site, not per user. This solution allows us to do so, and `user_data` is generic enough to possibly be of some use to others in the future.

@czue I am not entirely sure which would be the best place to put the code inside the location form. If there's a better way to approach this, then please elaborate.