Use Redis for Socket.IO sessions, instead of Socket.IO sessions

[mawoka-myblock]

This would dramatically improve reliability.

Requirement: Unique ID for every browser, decoupled from the Socket.IO id. Maybe generated on join and put into the URL or localStorage to survive a page reload reliably

[mawoka-myblock]

Okay, this is basically done, BUT there are mentions throughout the whole part where the sid is used for different purposes, should not be done like that if possible to achieve the long-term goal of surviving network interruptions and page reloads.