IMS-VT: FR36165 - UI renders after receiving video frame

- Show far end video after receiving the first video frame

- IMS notifies us when it receives the first video frame
  through the PLAYER_START event. Show incoming video
  once we receive this event

- When frames stop transmitting, IMS notifies us through
  the PLAYER_STOP event. Hide the incoming video once
  we receive this event

Change-Id: Ibdd001679d08cd5dbefd2f944ac97597897bcc51
CRs-Fixed: 1051225