Add ability to watch multiple streams (don't kill current streamlink on second run)

[the1ts]

Allows the user to run multiple streams, either by default or asking each time.

• Add optional MULTIPLE config item and _multiple function
• If MULTIPLE not set, then killall as usual
• If MULTIPLE set to true, don't killall
• If MULTIPLE set to ask, checks for running streamlink, if found asks for input.

[the1ts]

I was unsure how to handle updating of the config file on addition of new config items since the user updates the file manually for the OAuth token, stream, player and chat application at this time, hence the handling of not being set at all.

I guess if the variable does not exist in the config file, rofi could be used to get a decision from the user and append to the config file. I can work on that if it sounds sensible or required.

This brings up another piece I'm working on, namely, updating chat application to allow none (without error) or chrome/firefox popout chat in app/kiosk mode (no browser UI). This could use the same method to use rofi to question user and update mechanism on first use.

[jp1995]

Yeah these prompts should be good.

As for the last bit, the error is really just like a reminder for first time launch. I assume kpl is mostly bound to a key combination and the error doesn't show up at that point. It's pretty minor but perhaps can be improved. Popout chat seems good.