Merge branch 'cal-activities-target-reference' into 'master'

Changes calendar activities to use target reference

## What does this MR do?

Uses the targets reference in the calendar activities list. Previously it was using `#` which is wrong for merge requests.

## Screenshots (if relevant)

![Screen_Shot_2016-06-29_at_14.29.08](/uploads/4c52bbc7ca68d7b25e5bfb11ea55eef7/Screen_Shot_2016-06-29_at_14.29.08.png)

See merge request !4992

app/views/users/calendar_activities.html.haml

@@ -14,7 +14,7 @@
         - else
           = event_action_name(event)
           - if event.target
-            %strong= link_to "##{event.target_iid}", [event.project.namespace.becomes(Namespace), event.project, event.target]
+            %strong= link_to "#{event.target.to_reference}", [event.project.namespace.becomes(Namespace), event.project, event.target]
 
         at
         %strong