checks: Add is_broadcaster check to PartialChatter class.

[adambirds]

Pull request summary

I have added the is_broadcaster check to the PartialChatter class so that it is accessible at ctx.author.is_broadcaster. This checks for the presence of the broadcatser badge within the badges received in PRIVMSG.

Checklist

• [x] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes.
  • [x] I have updated the changelog with a quick recap of my changes.
• [ ] This PR fixes an issue.
• [x] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[EvieePy]

Thanks