Command integration with Nightbot/StreamElements

[olivermrose]

Checklist

• I have searched the existing issues to make sure this feature hasn't already been requested.

Describe the Feature

Continuation of #73, lower priority. Nightbot and StreamElements are the only two bots that I know that have a public API to retrieve channel commands, so that's why I'm focusing on them.

• Nightbot integration
  • Fetch user id through https://api.nightbot.tv/1/channels/t/{username} and then make a request to https://api.nightbot.tv/1/commands with the nightbot-channel header set to the id
• StreamElements integration
  • Fetch user id through https://api.streamelements.com/kappa/v2/channels/{username} and then make a request to:
    • https://api.streamelements.com/kappa/v2/bot/commands/{id}
    • https://api.streamelements.com/kappa/v2/bot/commands/{id}/default