comments: add standalone new comment form.

Add standalone /comments/new page to allow commenting if javascript is
disabled.

app/controllers/comments_controller.rb

@@ -106,6 +106,6 @@ private
     permitted_params += %i[is_deleted] if context == :update
     permitted_params += %i[is_sticky] if CurrentUser.is_moderator?
 
-    params.require(:comment).permit(permitted_params)
+    params.fetch(:comment, {}).permit(permitted_params)
   end
 end

app/views/comments/new.html.erb

@@ -0,0 +1,13 @@
+<div id="c-comments">
+  <div id="a-new">
+    <h1>New Comment</h1>
+
+    <%= render "comments/form", comment: @comment %>
+  </div>
+</div>
+
+<%= render "secondary_links" %>
+
+<% content_for(:page_title) do %>
+  New Comment - <%= Danbooru.config.app_name %>
+<% end %>

app/views/comments/partials/index/_list.html.erb

@@ -27,7 +27,7 @@
 
   <% if CurrentUser.is_member? %>
     <div class="new-comment">
-      <p><%= link_to "Post comment", new_comment_path, :class => "expand-comment-response" %></p>
+      <p><%= link_to "Post comment", new_comment_path(comment: { post_id: post.id }), :class => "expand-comment-response" %></p>
       <%= render "comments/form", comment: post.comments.new, hidden: true %>
     </div>
   <% end %>