Improve influence comment handling.

Improve influence comment handling.

This adds a number of form classes for commenting, which allow to choose
between public or private comments and can prevent the choice of markup.
Using a wrapper function, the right class can be selected depending on
the logged in user and the comment to reply to.

Each comment to display is annotated with the reply form to reply to it,
so we no longer need changes in threaded_comments to support quoted
replies.

Additionally, a new view is added that handles the selection of the
right form class when saving a comment.