Improve session management

[hellopablo]

Session management in Nails is a little convoluted. New sessions are generated quickly, and garbage collection tends to miss things.

Session management should be revisited so as to consider the following:

• More robust session handling, and ID generation
• If logged in, sessions should be tied to the user
• App should be able to show users which sessions are active (and rough location)
• App should be able to log a user out of all sessions remotely, or even a specific session