Rename to `WebfactoryMatomoBundle` (GH) and webfactory/matomo-bundle (Composer)

Piwik has been re-branded to Matomo, and it's likely going to stay that way.

So, how can we reflect this here and rename the Bundle, without causing too much headache or even breakage for our users?

Some initial pointers at https://stackoverflow.com/questions/55378780/how-to-rename-a-php-package-in-packagist.

Does anyone see how that could break things?