Feature Suggestions: allow "_comment" in {%- schema -%} attributes

[ckanitz]

So {%- schema -%} can get very bloated and hard to read, even with proper "id"s and since it's just JSON there is no native possibility to comment it.

Therefor I suggest to allow something like "_comment" as attribute within schema:

{
  "_comment": "-- NEWSLETTER SETTINGS --",
  "type": "header",
  "content": "t:sections.footer.settings.newsletter.settings_header.content",
  "info": "t:sections.footer.settings.newsletter.settings_header.info"
},
{
  "type": "checkbox",
  "id": "newsletter_enable",
  "default": true,
  "label": "t:sections.footer.settings.newsletter.enable.label"
},
{ "...": "..." }