Add an Event's target's title to its reference link

Given an activity feed entry like:

> Douwe Maan commented on [issue #123] at [gitlab-org/gitlab-ce]

...the `issue #123` link will now have a `title` attribute.

app/helpers/events_helper.rb

@@ -162,7 +162,7 @@ module EventsHelper
           "#{event.note_target_type} #{truncate event.note_target.to_reference}"
         end
       else
-        link_to event_note_target_path(event) do
+        link_to event_note_target_path(event), title: event.target_title do
           "#{event.note_target_type} #{truncate event.note_target.to_reference}"
         end
       end

app/models/event.rb

@@ -80,7 +80,7 @@ class Event < ActiveRecord::Base
   end
   def target_title
-    target.title if target && target.respond_to?(:title)
+    target.try(:title)
   end
   def created?

app/models/note.rb

@@ -19,6 +19,7 @@ class Note < ActiveRecord::Base
   delegate :gfm_reference, :local_reference, to: :noteable
   delegate :name, to: :project, prefix: true
   delegate :name, :email, to: :author, prefix: true
+  delegate :title, to: :noteable, allow_nil: true
   before_validation :set_award!

app/views/events/event/_common.html.haml

@@ -4,7 +4,7 @@
     = event_action_name(event)
   - if event.target
-    %strong= link_to event.target.reference_link_text, [event.project.namespace.becomes(Namespace), event.project, event.target]
+    %strong= link_to event.target.reference_link_text, [event.project.namespace.becomes(Namespace), event.project, event.target], title: event.target_title
   = event_preposition(event)