Finish renaming Piwik to Matomo everywhere #12420

In January 2018 we announced that Piwik is now Matomo :tada:

As part of the renaming efforts we're updating all our websites, tools, core app, plugins, ie. everything!

Renaming checklist left to do:

• [ ] make the build files matomo.zip and matomo.tar.gz, as well as the directory inside the builds should be called matomo
• [ ] plugin CustomPiwikJs to be renamed eg. CustomJsTracker
• [ ] plugin AnonymousPiwikUsageMeasurement to be renamed
• [ ] HTTP Tracking API endpoints: piwik.js and piwik.php
• [ ] JavaScript tracking sdk with objects like Piwik and window.Piwik and methods like getPiwikUrl
• [ ] Plugin developers, core platform uses namespace Piwik + some objects called "Piwik", an event Piwik.getJavascriptCode
• [ ] cookie names eg piwik_auth
• [ ] URL parameter like piwik_campaign to also support matomo_campaign
• [x] HTTP API methods eg. ExampleAPI.getPiwikVersion -> 3.3.0
• [x] DB prefix like piwik_ -> 3.3.0
• [ ] Remove --piwik-domain console parameter (see #13192) - Maybe in Matomo 5.0.0?
• [ ] After a successful auto-update, the screen shows Piwik is now Matomo and a big image. Be good to remove both.
• [ ] Marketplace URL parameters like "piwik_version"
• [ ] plugin.json parameters like require "piwik"
• [ ] CSS classes etc
• [ ] angular directives like piwik-foobar
• [ ] Remove Piwik font (already "renamed" to Matomo in #12489)
• [ ] Tracker proxy: Add matomo.php with keeping BC + Update [faq])https://matomo.org/faq/how-to/faq_132/) https://github.com/matomo-org/tracker-proxy/issues/55
• [ ] ... and more

In the case of Matomo core platform we want to keep things backward compatible for users including HTTP APIs users or users of the JavaScript SDKs.

Assigning to Matomo 4.0.0 but hopefully we can tackle a few of the list, and make progress on the others, during Matomo 3.x :rocket:

Hey there,
not sure if there's a separate repo for the website (matomo.org, didn't found one), but I think it will fit in here.

On the main page, there's this animation:

On the truck it say's Piwik, so that should be changed at one point in the future. :-)

Cheers!