This reverts commit 5f590f48cd.
In the end, a service is needed: The addon is ended when kodi starts playing the file, so the
downloader thread would be ended also. I need to launch the downloader thread from something that
isn't expected to end, which is why services exist.
First Proof-Of-Concept:
The addon notably lacks the ability to browse a peertube instance, and
it is not able to download torrent in the background (so they are almost
never completly downloaded as the downloas stops when kodi starts playing
the media).