Co-authored-by: Juliusz Chroboczek <jch@irif.fr>

Reduce button size and reduce video control bar size.
Add a volume slider to control volume level when volume control is enabled

There is no text on mobile layout

This was causing us to lose connections.

This simplifies the interface since close does the right thing
without help from the application.  Also improves error checking.

We now treat local and remote candidates differently, and flush
local candidates immediately after sending an offer.

This avoids a race condition if the group changes before the connections
are pushed.

Solves the issue of groups with a name ending in "/".

This was broken when we eliminated the login message.

To prevent size of menu to change when user click on present the unpresent button

The login message is replaced with handshake, which only carries
the client id.  Username and password is now in the join message.
Permissions is replaced with joined.

Input elements have no contents.  Thanks to Antonin Décimo.

The best TSDoc type is (Text|HTMLElement)[], but to JSDoc the array is
not distributive. JSDoc prefers Text[]|HTMLElement[], but TSDoc
rejects that syntax. In the end, both are fine with
Array.<Text|HTMLElement>.

Also get rid of dead groups, they're not useful.