Merge branch 'issue-boards-nav' into 'master'

Add boards controller to issue nav item

#### What does this MR do?
Adds active state to top level nav

Before: 
![Screen_Shot_2016-08-18_at_7.56.56_PM](/uploads/c5db0e9e077f0970b6b7b7d8d7a08147/Screen_Shot_2016-08-18_at_7.56.56_PM.png)

After:   
![Screen_Shot_2016-08-18_at_7.56.10_PM](/uploads/6b46e6f093c02fb44e25cf6952638a5b/Screen_Shot_2016-08-18_at_7.56.10_PM.png)


See merge request !5883

app/views/layouts/nav/_project.html.haml

@@ -65,7 +65,7 @@
             Graphs
 
     - if project_nav_tab? :issues
-      = nav_link(controller: [:issues, :labels, :milestones]) do
+      = nav_link(controller: [:issues, :labels, :milestones, :boards]) do
         = link_to namespace_project_issues_path(@project.namespace, @project), title: 'Issues', class: 'shortcuts-issues' do
           %span
             Issues