Adds an optional title attribute to polls. The rationale for this addition is that polls themselves didn't contain context/question and relied on post body to explain them. That context wasn't always obvious (e.g. when there are multiple polls in a single post) or available (e.g. when you display the poll breakdown - you see the answers, but not the question)
As a side note, here's a word on how the poll plugin works:
> We have a markdown poll renderer, which we use in the builder UI and the composer preview, but… when you submit a post, raw markdown is cooked into html (twice), then we extract data from the generated html and save it to the database. When it's render time, we first display the cooked html poll, and then extract some data from that html, get the data from the post's JSON (and identify that poll using the extracted html stuff) to then render the poll using widgets and the JSON data.
The poll breakdown modal replaces the grouped pie charts feature.
Includes:
* MODAL: Untangle `onSelectPanel`
Previously modal-tab component would call on click the onSelectPanel callback with itself (modal-tab) as `this` which severely limited its usefulness. Now showModal binds the callback to its controller.
"The PR includes a fix/change to d-modal (b7f6ec6) that hasn't been extracted to a separate PR because it's not currently possible to test a change like this in abstract, i.e. with dynamically created controllers/components in tests. The percentage/count toggle test for the poll breakdown feature is essentially a test for that d-modal modification."
