Add session support (stored in MongoDB, with signed cookies for sessionId)

Messed up the code a bit, since partially transitioning in an express-like structure, with app and middlewares. This will need to be cleaned. I do not use express itself, nor connect, but a custom implementation for now, for learning purposes. I will see how that turns out.
It has been pretty tricky to plug the express-session and cookieParser on my custom App. Again, cleaning will come later.

IMPORTANT NOTE: sensitive config should be placed in src/server/env/config.json
This file is .gitignore'd, and there is a default config provided. But a specific config.json need to be put on the prod server.
Make the admin edit work.

Allow login. Sample user to add in 'users' collection: { "login" : "john", "pwd" : "secret", "isAdmin" : true }
Plug the access (http request/response) and business (data handling) together.
Updated all routers and views to use the (request, response, ctx) interface (ctx is where ctx.db is).

IMPORTANT NOTE: db schema updated (matches/goalaverage changed to matches/goal_difference)
Release version v0.4.0