Adapt watch.html path to current RWTH moodle

There are at least //paella/ui and /paella7/ui, so we just remove the hard-coded path and match every path in engage.streaming.rwth-aachen.de.

Fixes #2

free.js

 if (window.location.host === 'engage.streaming.rwth-aachen.de') {
-  if (!window.location.href.startsWith('https://engage.streaming.rwth-aachen.de/paella/ui/watch.html'))
-    console.warn('looks like we are running outside a player context‽')
-
   const inFrame = (window.parent !== window)
   const vId = new URLSearchParams(location.search).get('id')
   fetch(`https://engage.streaming.rwth-aachen.de/search/episode.json?${new URLSearchParams({id:vId}).toString()}`)