Remove single alias/implication requests.

* Remove the single alias and implication request forms. From now
  on, bulk update requests are the only way to request aliases or
  implications.

* Remove the forum topic ID field from the bulk update request form.
  Instead, to attach a BUR to an existing topic you go to the topic then
  you click "Request alias/implication" at the top of the page.

* Update the bulk update request form to give better examples for the
  script format and to explain the difference between aliases and
  implications.

app/models/tag_alias.rb

@@ -23,7 +23,7 @@ class TagAlias < TagRelationship
         ForumUpdater.new(
           forum_topic, 
           forum_post: post,
-          expected_title: TagAliasRequest.topic_title(antecedent_name, consequent_name),
+          expected_title: "Tag alias: #{antecedent_name} -> #{consequent_name}",
           skip_update: !TagRelationship::SUPPORT_HARD_CODED
         )
       end

app/models/tag_implication.rb

@@ -202,7 +202,7 @@ class TagImplication < TagRelationship
       ForumUpdater.new(
         forum_topic, 
         forum_post: post, 
-        expected_title: TagImplicationRequest.topic_title(antecedent_name, consequent_name),
+        expected_title: "Tag implication: #{antecedent_name} -> #{consequent_name}",
         skip_update: !TagRelationship::SUPPORT_HARD_CODED
       )
     end