Improvements for videoconference/audio calls/desktop sharing

[netdevfighter]

Your Rocket.Chat version: 0.24.0

I see some problem with this feature:

On Safari 9.1: I see the buttons for videoconference/audio etc. but I get no feedback after clicking the button. I know the reason is the missing WEBRTC but I think in this case is better to send a feedback message to the user.

General:

• It is not possible to add person in an ongoing video conference.
• Is it possible to have temporary video conference without the groups feature? We have very often a video conference with very different group of users.
• Is it not possible to switch between desktop sharing and video (After disabling the desktop sharing we get a black screen from the person).

I think this all.

[engelgabriel]

As part of the https://github.com/RocketChat/Rocket.Chat/issues/933

[flantascience]

Is this working now?

We're struggling to get video conferencing working on Safari on Mac.