Adding Piwik as a analytics option

[jloh]

As requested here (https://meta.discourse.org/t/support-for-piwik-analytics-as-an-alternative-to-google-analytics/7512/51) by several people this allows people to use Piwik as an alternative to GA.

I don't know if this PR will be accepted, but I'm hoping for it to be part of the Discourse core as opposed to having to build a plugin for this functionality.

I haven't updated all the languages, do I need to? Apologies if I've missed something else.

[coding-horror]

I really do not support this. Adding piwik is as easy as going to admin, customize, html and pasting the embed code in the html footer.

[jloh]

I don't know why the build failed, it seems to be unrelated to any of the changes I made.

Also, doing it this way adds the functionality that you give people with GA by pushing custom variables. I'm not sure this is possible with the footer method?

[SamSaffron]

@coding-horror the footer thing don't trivially work cause you need to integrate with the page tracker, I do dislike the coupling of yet another tracking mechanism into our code base beyond the 2 google ones.

I wonder if longer term having a public browsable library of site customisations is the way to go, cause then core does not need to get infected with this.

[jloh]

Closing PR are further discussion on the above linked thread.