WIP: Updating Advanced/Player/Multiple instances

Hello @Garf. I ran into some trouble while working on a branch and I wasn't able to solve it after two hours of trying. I thought I would delete the old fork, fork the original repo again, do the new work on it and that would fix the issue. It was a bad decision in hindsight, as the old merge requests got deleted too. I apologise for the inconvenience.

This updates #7, updated from https://wiki.videolan.org/How_to_play_multiple_instances_of_VLC/