Update server.js - add registration feature

* add _registration_date to User class
* add methods documentation
* fix UsersDatabase constructor (now use synchronized version of
* fs.exists)
registration fix
registration fix
Add User::strip_object() method
starting conference implementation.
Merge branch 'develop' of https://github.com/Regalis/Jamii into conference
Update server.js - store socket object instead of socket.id
Merge branch 'develop' of github.com:matteozajac/Jamii into develop
conrefence class
Fized merge conflicts with Regalis/develop

Conflicts:
	src/server.js
Fixed registration on client side.