res_pjsip_outbound_registration.c: Use our own scheduler and other stuff

* Instead of using the pjproject timer heap, we now use our own
  pjsip_scheduler.  This allows us to more easily debug and allows us to
  see times in "pjsip show/list registrations" as well as being able to
  see the registrations in "pjsip show scheduled_tasks".

* Added the last registration time, registration interval, and the next
  registration time to the CLI output.

* Removed calls to pjsip_regc_info() except where absolutely necessary.
  Most of the calls were just to get the server and client URIs for log
  messages so we now just save them on the client_state object when we
  create it.

* Added log messages where needed and updated most of the existong ones
  to include the registration object name at the start of the message.

Change-Id: I4534a0fc78c7cb69f23b7b449dda9748c90daca2