Streamline adding KBD to a channel

Currently adding KBD to a channel requires going to a channel where KBD is already watching, issuing it a join command, and then giving it moderator powers. This is kinda awkward from a UI/UX perspective.

Instead, a preferable UI/UX might be:

• The user visits a web-page for KBD and presses a button to add it to their channel
• The user is redirected through a Twitch authorization flow to authorize KBD
• There is no step 3

In the behind-the-scenes:

• KBD exposes a callback endpoint for an authorized token
• Receiving that token, it:
  • Makes itself moderator on the channel associated
  • Joins itself to the chat of the channel associated

Additionally, the page for "add KBD to the channel" can be static.