Add visitor tracking to all pages

[nuest]

We must add visitor tracking to the page so that we know from which devices, countries and reacting to which other pages our visitors come to envirocar.org.

Task: add PiWik tracking code to https://github.com/enviroCar/enviroCar-www/blob/master/footer.php

@bpross-52n Can you coordinate that with it-support?

[bpross-52n]

We now have a piwik overview page for enviroCar.org and also the code to integrate in the footer. IT-IS mentioned privacy issues. We could add an iframe, so users could opt-out and they will no be tracked anymore. This is working with a cookie. Should we add this iframe? If yes, where?

[nuest]

Do we need a cookie policy to set this cookie :-). I've just been seing many of these "We use cookies" pop-ups...

Opting-out seems good, the message could be displayed with the regular messaging architecture (@MartinDueren might be able to point us to the right spot when he is back from holidays).

[bpross-52n]

I think this cookie is ok, its only job is to prevent us from tracking :) However, with a general "We use cookies" pop-up we would be on the safe side, I'd also like to give the users information about all the cookies our page leaves on his system. https://www.envirocar.org/terms.php#cookies is outdated.

[nuest]

Ok - I think it would be easiest to keep the information up to date on the website instead of maintaining another resource about this, so maybe you can outline the update here and then we edit the dev branch.

By the way, the Mag Pi has a nice cookie pop-up, see the bottom right: http://www.themagpi.com/issue/issue-19/

[EHJ-52n]

@nuest @bpross-52n I have sent @matthesrieke a mail with all required details. He will take care of this as ordered by @staschc.