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 .
To reduce waste pop_back(), how about using the following way.
1) Make a ActionDef instance body instead of calling push_back() and getting the reference at the top of this block.
2) Call actionDef.push_back(actionDef) when userIdSet.isValidActionOwnerId() is true at here