Merge branch 'add-meta-referrer-tag' into 'master'

Add meta tag for referrer

https://gitlab.zendesk.com/agent/tickets/7054

Added a meta referrer tag, so that only the origin is sent to third party sites, instead of the entire URL, thus avoiding the leak of sensitive information like password reset tokens.

/cc @DouweM

See merge request !1263

app/views/layouts/_head.html.haml

@@ -3,6 +3,7 @@
   %meta{charset: "utf-8"}
   %meta{'http-equiv' => 'X-UA-Compatible', content: 'IE=edge'}
   %meta{content: "GitLab Community Edition", name: "description"}
+  %meta{name: 'referrer', content: 'origin'}
   %title= page_title