Add modals for "Reply"

[ejucovy]

Not strictly a workflow action button, but I'd like to add a modal to the "Reply" buttons next to each comment and next to the ticket description.

I think this could just open a modal with a comment form, prefilled with the quoted comment text, and with the workflow action set to "Leave" (or more properly, a configurable value defaulting to leave)

I need to double check how trac comment replying actually works though; it's possible an extra parameter is sent in the post request to set the threading.