Save streams representation to the database

[sneakycrow]

• Adds a representation of a "Stream" in the database, which starts out as an Entity with a start time, end time, and a link to a full event log.
• Adds support to the webhook callback for twitch to support stream.online and stream.offline for the Event Stream
• Adds support to the webhook callback event to save a new "Stream" when receiving a stream.online event
• Refactors workers module into new queue, stream, vendor, and event modules