Merge branch 'fix-print-css' into 'master'

Hide UI elements when print md files or wiki pages

Fixes #1023

See merge request !416

app/assets/stylesheets/print.scss

@@ -11,3 +11,7 @@ header, nav, nav.main-nav, nav.navbar-collapse, nav.navbar-collapse.collapse {di
 .wiki h1 {font-size: 30px;}
 .wiki h2 {font-size: 22px;}
 .wiki h3 {font-size: 18px; font-weight: bold; }
+
+.sidebar-wrapper { display: none; }
+.nav { display: none; }
+.btn { display: none; }