thread polls support

[liesandfish]

no code yet because this depends on #813 (in part because it's going to bump the DB version again but also because I foolishly put all the constants/etc right next to the mod tools ones)

but I wanted to get this (empty for now) PR open to get your thoughts on it since the code is probably less exciting to review than the actual UI changes made. when mod tools get merged I'll shove all the code in here and unmark as draft

doesn't support adding a poll to a new thread, since that's a different pile of work that's less frequent

you're looking at (any page in) a thread and it has a poll you haven't voted on:

you click on the cool new poll button (i trimmed as much horizontal dead space as i could without ruining the button's hitbox, but yes the threads with a poll do have a slightly shorter title bar as a result - still a lot better than SA in the browser where there's a bigass box at the top of every page lol)

you pick your option (or options if the poll is one of the multi-pick ones) and then you click VOTE

now when you go back to that thread, the icon is less in-your-face

and you can still click on it to see the results

(you may be wondering why i posted another screenshot of the results page, well... for vbulletin reasons they're apparently slightly different HTML depending on if it's the one embedded in the page or the one you get after voting lol)

so yeah, if you have feedback about the design while the mod tools PR is still pending, let me know and i can incorporate it, otherwise i'll just wait for mod tools to be merged and then i'll update this PR with the code

[Sereri]

#813 is merged, this looks great. I'm mildly mad at myself for not thinking of "hiding the poll behind a toolbar button".