Merge branch 'username-issue-header' into 'master'

Added username to issue & merge request header

Closes #13771 

## Issue header

![Screen_Shot_2016-03-01_at_16.59.32](/uploads/a112dfb91eb9b6f911c716265b35043c/Screen_Shot_2016-03-01_at_16.59.32.png)

## Merge request header

![Screen_Shot_2016-03-01_at_16.59.26](/uploads/67bf9e65ac5cae4667db6c5148cb57a0/Screen_Shot_2016-03-01_at_16.59.26.png)

See merge request !3048

app/views/projects/issues/show.html.haml

@@ -29,6 +29,7 @@
       %span.creator
         ·
         by #{link_to_member(@project, @issue.author, size: 24)}
+        = '@' + @issue.author.username
         ·
         = time_ago_with_tooltip(@issue.created_at, placement: 'bottom', html_class: 'issue_created_ago')
 

app/views/projects/merge_requests/show/_mr_title.html.haml

@@ -6,6 +6,7 @@
   %span.creator
     ·
     by #{link_to_member(@project, @merge_request.author, size: 24)}
+    = '@' + @merge_request.author.username
     ·
     = time_ago_with_tooltip(@merge_request.created_at)