app_queue: Fix a few member pause bugs

* Always set member->lastpause when setting member->paused

* Fixed typo (using member->lastcall instead of member->lastpause) in
  'queue show' output.

* Use a constant 'now' in 'queue show' output for a better point-in-time
  view of time based stats.

ASTERISK-27541 #close
Reported by: César Benjamín García Martínez

Change-Id: Ib41ced90cfdb66f9bb1e7b263d0f6fc1ac6e18fa