MDL-58492 icons: Fix fontawesome for i/marker and i/marked icons

These combo icons are used to mark something the current element. They
are supposed to be used in places like the course outline to
mark/highlight a section as the current one. Also workshop uses them to
switch to a phase (mark it as the current one).

lib/classes/output/icon_system_fontawesome.php

@@ -287,8 +287,8 @@ class icon_system_fontawesome extends icon_system_font {
             'core:i/log' => 'fa-list-alt',
             'core:i/mahara_host' => 'fa-id-badge',
             'core:i/manual_item' => 'fa-square-o',
-            'core:i/marked' => 'fa-check-square',
-            'core:i/marker' => 'fa-user-o',
+            'core:i/marked' => 'fa-circle',
+            'core:i/marker' => 'fa-circle-o',
             'core:i/mean' => 'fa-calculator',
             'core:i/menu' => 'fa-ellipsis-v',
             'core:i/mnethost' => 'fa-external-link',