Re-implement !pb2uptime using new helix endpoint

[RAnders00]

Helix has this new endpoint:

https://dev.twitch.tv/docs/api/reference/#get-streams

Which allows the bot to fetch the uptime without the ridiculous stream webhook system

[pajlada]

I would like the uptime command to work the same way it works in pajbot1, where if a user goes live, streams for an hour, restarts OBS to change resolution, streams another hour, then a user types !uptime it returns 2 hours, not 1 hour. Not sure if that is possible if we just use the "started_at" time in this API