Code Cleanup: Usage of Polymorphic User instead of ExternalUser and InternalUser

Renamed requestor_user_id -> user_id
Index of request_for_comments now returns the n (5?) newest requests per user. Solved via sliding windows in postgres, code added to model.
Added route to /my_request_for_comments/ that shows all requests for the current user.
Changed view from ERB to slim

db/migrate/20150903152727_remove_requestor_from_request_for_comments.rb

@@ -0,0 +1,5 @@
+class RemoveRequestorFromRequestForComments < ActiveRecord::Migration
+  def change
+    rename_column :request_for_comments, :requestor_user_id, :user_id
+  end
+end