Add support for polls

[connyduck]

mastodon/mastodon#10111

I have not yet looked at it and I really hope its not a breaking change that will crash Tusky.
But we definitely need to add support for displaying polls and voting very soon.
Creating polls can wait some time, but we of course we will also add that feature.

[connyduck]

I will do this in three parts:

1. polls in timelines & voting
2. polls in notifications
3. creating polls

1 is about 60% finished

[rinpatch]

Would be nice if poll creation used poll_limits object from /api/v1/instance used by glitch-soc and (soon) pleroma instead of depending on hardcoded values