First party cookie with server side store #2680

With the implementation of first party cookies in #409, the reliance on client-side cookie storage is growing. This is causing problems where sites are using multiple trackers and/or amassing more content in the cookie.

Requirements:

• a single client side cookie per tracking server
• server-side storage for the bulk of the corresponding cookie's contents
• ability to track multiple site IDs

Benefits of a smaller cookie:

• lowers risk of failed tracking requests; less overhead in the HTTP request
• less data exposed to third-parties who peek into document.cookie

Impact:

• database: increased storage requirements; slower tracker performance; requires a cleanup mechanism (to mimic cookie expiry)
• this is not going to be backwards compatible; so targeting for Piwik 2.0

Misc:

• piwik.js has become somewhat bloated; also, while the coding convention used allows for true private variables, JavaScript coding practices have moved towards the prototype model; so, we may want to consider this for a rewrite
• the js/ proxy could browser sniff, and serve out a smaller version of piwik.js which uses the browser's native JSON (e.g., FF3.5+, IE8+; not sure about Safari/Chrome/Opera)

I thikn such work would be included in this ticket: #2750 Life Time Value of a customer (which will require a visitor store to keep of track of lifetime values)