Csrf prevention

Added simple csrf prevention to fix issue #5 (closed) :

• The server generates a random, unique csrf token, stores it in the session and appends the token on the map and admin pages
• The token is added to every POST, PUT and DELETE request inside 'x-csrf-token' header
• Likewise, for every POST, PUT and DELETE request, the server checks that the token stored in the session matches the token from the header

changed the description

approved this merge request

merged

mentioned in commit f6546934