Fixes to prevent PHP notices

* Ensure "$sep" and $trickytopic are defined before they are used
Follow-up fixes to prevent PHP notices, plus undo previous fix

* Undo "$trickytopic" fix in "subject_summary" shortcode class - not used
* PHP notice fix for wp-admin - Add new tricky_topic - below location field
* Add style/ CSS for <h3> subject-list
Merge pull request #3 from IET-OU/master

Fixes to prevent PHP notices