feat(activities): handle and kill multiple chat process ids

[Zibbp]

Resolves #437

[russelg]

I've been thinking about this a bit. Wouldn't it be better to match on the chat output path rather than the stream name when we kill chat downloader?

[Zibbp]

That's a good point. No other linux process uses the temporary chat file so it should be find to search by justthe tmp chat file path, instead of the just the channel or even the full process (chat_download https://twitch.tv/foo --output /tmp/foo.json).