Allow links and images on legislation drafts

Note we're using a new sanitizer. Ideally we'd reuse the
`AdminWYSIWYGSanitizer`, but then code that would be correctly shown by
markdown-it (like the <h1> tag) wouldn't be shown on the web, which is
confusing. Ideally we would configure markdown-it to only allow the tags
present in the `AdminWYSIWYGSanitizer` and provide some kind of help
showing which tags are allowed.

app/helpers/application_helper.rb

@@ -25,7 +25,7 @@ module ApplicationHelper
       superscript:        true
     }
 
-    sanitize(Redcarpet::Markdown.new(renderer, extensions).render(text))
+    AdminLegislationSanitizer.new.sanitize(Redcarpet::Markdown.new(renderer, extensions).render(text))
   end
 
   def wysiwyg(text)

app/views/legislation/draft_versions/show.html.erb

@@ -57,7 +57,7 @@
 
         <div data-sticky-container>
           <div data-sticky data-anchor="sticky-panel" class="draft-index sticky" data-tree-navigator>
-            <%= sanitize(@draft_version.toc_html) %>
+            <%= AdminLegislationSanitizer.new.sanitize(@draft_version.toc_html) %>
           </div>
         </div>
       </div>
@@ -74,7 +74,7 @@
                    data-legislation-annotatable-base-url="<%= legislation_process_draft_version_path(@process, @draft_version) %>"
                    data-legislation-open-phase="<%= @process.allegations_phase.open? %>">
           <% end %>
-            <%= sanitize(@draft_version.body_html, { attributes: ["id"] }) %>
+            <%= AdminLegislationSanitizer.new.sanitize(@draft_version.body_html) %>
           </section>
         </div>
       </div>