Set proper title in players windows

[Sheraff]

Right now, peerflix simply starts the players (only tested on VLC and MPV) thus the title shown is usually something like http://localhost:8888/ but most players have simple options to set the window title to anything. IMO, it would be fitting to set it to the name of the file being played.

This is a simple improvement to add. I'll do it if I find the time, but anyone else is welcome. Perfect for 1st contribution as well.