Fix memory leak

[dasaderi]

There is a bug in the code that makes it so that sometimes when users go on it crashes.

[dasaderi]

Not needed if we move code to Azure account (see issue #75).

[blahah]

I don't think the memory leak issue is related to the cloud provider. It will be somewere in the server code, and will happen the same on Azure.

[dasaderi]

Update after call with WinGravity:

PRE doesn’t use a session store yet so Sebastien think that’s the issue.
 Sessions are done with https://github.com/expressjs/session
in. Rapid uses Redis for the session store.


[blahah]

Very true that the default session store will leak memory, and that should be solved.

I doubt that it's the sole reason for the memory accumulation which is quite rapid: sessions are tiny and the number of users is not enough to account for it. I'd also argue that given the scale of the project, for PREreview at least, Redis is overkill. Just a simple file, leveldb or sqlite would be fine, are trivial to implement, cost nothing to run, and use a tiny fraction of the resources.