Merge branch 'rs-event-common-has-tooltip' into 'master'

Add tooltips for common Event feed entries

This adds tooltips to the event target for events like "opened merge
request !XYZ"

After https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4090#note_11712839, several references in the event feed had titles but were still missing tooltips.

See merge request !4371

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], title: event.target_title
+    %strong= link_to event.target.reference_link_text, [event.project.namespace.becomes(Namespace), event.project, event.target], class: 'has-tooltip', title: event.target_title
 
   = event_preposition(event)