* Adds package that can configure using turnserver for jitsi-meet.

Activates http2 on the nginx host and uses the alpn send with the web requests to multiplex traffic to be served as web of proxied to the turn server.
It needs nginx at least v1.13.10.
Adds turncredentials module from Philipp Hancke, with small modification (all int values for hosts need to be strings/tostring()) in order to be able to use the module with prosody 0.11.

* Moves loading of stream after loading stream module (50-..).

* Leaves DISABLE_TCP_HARVESTER to be handled by jvb.

* Fixes comments.

* Properly detect first time coturn install and configure it.

* Handles upgrading from jetty serving web.

* Does not create jvb user if already exists.

* Fixes let's encrypt and adds turnserver handling.

* Enables use of turn server in config.js if available.

* Adds a check whether prosody config exists.

There are cases where deployments can still have configured prosody in the main prosody config in /etc/prosody.

Now the web app can be installed separately from jicofo and jitsi-videobridge, or can be installed on machine running nginx or apache. Currently only nginx will be configured and apache config is left to user. Later we can add and the apache config. Renames jitsi-meet to jitsi-meet-web (just the web content) and jitsi-meet-web-config (configuring jetty, nginx or apache). A new jitsi-meet package will be introduced, a meta package depending on jicofo, jvb and the current packages.