Related to #49

- Tested if removeBinding() is called when the client lose the connection
  before issuing an unbind request
Related to #77

Implemented stats for user.httpapi

Remaining task:

- Implement stats showing in jcli
Related to #49

ANY PDURequest will set user's last_activity_at
Related #49

Testing inactivity on server side
Related to #49

Tested message transmission fidelity