Add support for polls in posts

[thunze]

This feature allows the user to add polls to statuses via the UI. 📊

Introducing polls required a bunch of changes and additions, so I’ll comment on a few to hopefully make them easier to understand. ☕

• A poll is added to a status in the same HTTP request to Mastodon that posts the status.¹
• A custom JSON deserializer for poll options was added because Mastodon returns them as objects in the HTTP response to posting a status with a poll.
• Some validation logic had to be introduced to ensure that only valid statuses can be created using autodone:
  • A status that has media cannot have a poll at the same time.
  • A poll must have at least 2 options.
  • A poll cannot have duplicate options. Leading and trailing whitespace must be removed from each poll option before validating this.
• I had some fun with the poll options UI. It looks and feels quite nice, but introduces a bit of JavaScript. If you’d rather like to avoid that, feel free to make the poll option fields static.

Note that I originally started implementing this feature by copying from how media support is implemented.

Footnotes

1. API docs: https://docs.joinmastodon.org/methods/statuses/#create ↩