Add classes to inline comments

There's not much other filtering we can do here in a theme compatible way, so
use classes for attaching.
Set the paragraph key directly

This is a much quicker way of setting the attribute, and ensures that we don't
have multiple accidentally (not sure if that could happen really)
Add the inlinecomments-enabled class to commentable paragraphs
Change inlinecomment-* to inlinecomments-*
Add first round of UI