UC-1445: Control voicemail playback

* Handle play and pause in freeswitch_voicemail
UC-1445: Control voicemail playback

* Assert play or pause playback status
UC-1445: Control voicemail playback

* Allow voicemail replay
UC-1445: Control voicemail playback

* Push mediastop event
UC-1445: Control voicemail playback

* Send mediaload on replay
Implement seek