Changing front-facing occurrences of `Piwik` to `Matomo`

[TheCrowned]

The plugin is officially called WP-Matomo, but there are multiple occurrences of WP-Piwik showing up in the WP admin dashboard when one installs the plugin the first time. I know a bit about the history of the project, so I know it changed name and that it was formerly Piwik, but it can be quite confusing to a new user who approaches the project now, and sees these two different names popping up.

An example:

Welcome to WP-Matomo, and Connect to Matomo, but then Settings for WP-Piwik.

It is true that the label can be renamed to whatever you wish, but I don't see a point in shipping an old name with newer releases: people who have had it for years can have the customized old Piwik name, if they wish, but at least to new ones it would be nice to be up to date :) Anyway, even with the label renamed, there is still quite some legacy naming around. Another example is the page title of the dashboard page:

And some more admin messages scattered around. I hope I have caught all instances of them. Please notice that this does not affect any class/backend naming - it's just public facing labels.

[braekling]

Same here, thanks for your support!