account: make sure the UPnP controller is updated correctly

1) Add an override of the updateUpnpController function in JamiAccount
   to ensure that all the shared pointers to an account's UPnP
   controller get updated together
2) Call updateUpnpController when an account gets enabled/disabled so
   that UPnP can be (de)activated immediately if necessary

GitLab: #988
Change-Id: I6ff5cefd285c37aa014aebbb862b7d7eb06aadb4