call: group call design: Design for group call (which is used for both group call and A/V conferences) has been improved to: - have a working fullscreen button; - have a better display of peer users in grid, with responsive design; - have a nicer design for peer user, and adding avatar/nickname as overlay on the bottom of the video stream; - add a way to (un)pin a peer user, which make is appear on the whole width on top of the grid. rel 448 HG<S-Insert>: changed sat_templates/templates/bulma/call/group_peer.html