Replace hardcoded domains in Mathoid APIs

[lens0021]

There are hardcoded domains and URI in Mathoid APIs, therefore a maintainer of a non-WMF wiki who wants to deploy Mathoid would replace those manually. [1] [2] [3]

Using the utils resolving domain and URI makes it easy to set RESTBase with Mathoid.

[1] https://phabricator.wikimedia.org/T154394#3356580 [2] https://www.mediawiki.org/w/index.php?title=Extension:Math/Restbase&oldid=4054010 [3] https://github.com/physikerwelt/mathoid-docs/blob/master/Guide%20for%20Installing%20and%20Setting%20up%20Mediawiki%20with%20Restbase%20and%20Mathoid.pdf