Allow playlists to be played from network

[zeroeightysix]

.m3u, .m3u8 (and probably txts as well) are frequently hosted on the web for TV stations, videos, and other media.

This PR checks if the "file path" starts with http:// or https://, and, if so, does not try to load those 'files' from filesystem.

Previously syncplay would not be able to load videos from the internet through the File > Open media stream URL menu as it'd try to load them from the FS.

[Et0h]

@zeroeightysix Would it be better to use the specific HTTP(S) check as proposed or the more generic utils.isURL protocol check which catches all :// paths?

[Et0h]

Syncplay is not designed to load .m3u and .m3u8 files directly, it leaves that to the media player.

If you have a specific use case that is improved by the change then please specify it in more details.

[zeroeightysix]

@zeroeightysix Would it be better to use the specific HTTP(S) check as proposed or the more generic utils.isURL protocol check which catches all :// paths?

I'm not sure. I guess this might allow videos to be played over ftp, or other protocols, but I question the practicality and support by media players to handle such URLs. Allowing any URL to be passed might also cause security concerns. (As in, is it possible to trick users into supplying a maliciously crafted URL to their media player, breaching security in any way?)

If you have a specific use case that is improved by the change then please specify it in more details.

I made this PR to solve mpv not being able to play a video (supplied as m3u over the network) through syncplay, while it was able to play the video if ran from the terminal (using mpv <URL>).
I could not find a way for syncplay to communicate to mpv that it was supposed to fetch & play a m3u file from the internet, hence this change.

I did not check for compliance with any other media player, for which my apologies.

[Et0h]

I tested the PR with mpv, mpv.net, VLC, MPC-HC (1.9.8) and it worked. As usual, streaming works best with Syncplay when using mpv/mpv.net due to how they handle seeks to areas which have yet to be buffered.

I used a Big Buck Bunny test stream:
https://multiplatform-f.akamaihd.net/i/multi/will/bunny/big_buck_bunny_,640x360_400,640x360_700,640x360_1000,950x540_1500,.f4v.csmil/master.m3u8