feat: Add support for POLL_RESULT messages

[DA-344]

Summary

Adds support for POLL_RESULT message types.

This also adds more things to Poll, such as Poll.victor_answer, exact vote count on Poll.total_votes, etc.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• 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, ...)

[DA-344]

Needs testing, if everything works then this would be ready.

[DA-344]

I have been testing the PR and it works, so it is ready for review.

[Rapptz]

This looks mostly okay I guess. I'm not sure how I feel about updating the state as a result of it but it's not too egregious so it can stay. It merely needs to document the new message type.