Merge branch 'mr-title' into 'master'

Add space under MR title

## What does this MR do?
Adds space underneath MR title because right now it's impossible to tell where the title ends and the first header of the MR body begins. 
Before:   
![Screen_Shot_2016-08-18_at_1.43.05_PM](/uploads/4e07892036b1d90217fdecbed31a9494/Screen_Shot_2016-08-18_at_1.43.05_PM.png)

After:    
![Screen_Shot_2016-08-18_at_1.42.22_PM](/uploads/1341d4d7c5bd0db21233f6ebb961bafc/Screen_Shot_2016-08-18_at_1.42.22_PM.png)


Note: We need to change our template to have the md headers `####` instead of `##`. Once that's been done it will look like this:
![Screen_Shot_2016-08-18_at_1.46.46_PM](/uploads/e30d432551debc15ec210e76dfcd3451/Screen_Shot_2016-08-18_at_1.46.46_PM.png)

See merge request !5875

app/assets/stylesheets/pages/merge_requests.scss

@@ -374,3 +374,10 @@
     }
   }
 }
+
+.merge-request-details {
+
+  .title {
+    margin-bottom: 20px;
+  }
+}