issue #107, Remove the Action of without owner.

When remove the "User", to remove the "access_list" together, but don't remove "actions". 
When displaying the "actions", to display only the "actions" that the user(owner) is exists. 
To delete the "actions", run the deletion process on a cyclic(example:3600sec(1h)), 
to remove an "actions" if there is no owner user.However, USER_ID_SYSTEM is excluded .
It's hard to recognize the value at a glance and the unit (sec, msec, or used?).

How about using the following style.
ACTION_DELETE_DEFAULT_INTERVAL = 3600 * 1000; // msec (1hour)