mod reports: enable reporting for members, add dmail reporting.

* Add ability to report dmails.
* Enable reports for comments, forum posts, and dmails.
* Allow Members to send reports.
* Don't allow users to report the same thing twice.

app/models/application_record.rb

@@ -421,6 +421,12 @@ class ApplicationRecord < ActiveRecord::Base
     end
   end
 
+  concerning :DtextMethods do
+    def dtext_shortlink
+      "#{self.class.name.underscore.tr("_", " ")} ##{id}"
+    end
+  end
+
   concerning :AttributeMethods do
     class_methods do
       # Defines `<attribute>_string`, `<attribute>_string=`, and `<attribute>=`