avoid empty div when no comments and no right to add comment. Remove spurious parameters from ajax place holder url.

cleanup/refactor/document comment form generation on the way

fix comment's form handling: don't put comments relation in hidden section, simply use an HiddenInput. Also fix new comment detection

use standard form validation instead of custom json controller's methods, support to apply the commment section component on entity not yet created (will be created with the comment)

[views/json] import dumps from cw.web (which handles the different possible dumps impl. depending on python version or external json packages)

also refactor comment oneline view on the way

refactor: no need for InlineCommentView, nicer id on comment forms. Also properly fix #473629: register/login link should appears on the top of the form when clicking "add comment"