Debian install instructions with IPv6, rfc5766-turn-server, https and encrypted signaling

Made instructions for installing on Debian stable. Changed from Restund to rfc5766-turn-server because of trouble with IPv6 clients, now works if IPv6 client needs to use TURN. Changed all signaling to SSL encrypted and HTTPS mandatory. Changed to use prosody-0.10 instead of trunk because of errors with MUC module in Prosody trunk which prevented password protecting rooms from working. Added instructions for enabling screen sharing in chrome without extension.

Added rfc5766-turn-server configuration example file.