Fix attribution in comments for "wp-evidence-hub" WordPress plugin PHP

* That is, link to Martin Hawksey/ @mhawksey on GitHub etc.
* Fix typo in README markdown
Add theme-specific styles to Wordpress plugin CSS - HACK!
Fix PHP notices about $post->sector_slug - defensive programming

* Test using "isset()"
Handle no post id for geomap - followup fixes

* Missing PHP "echo" etc.
Merge pull request #3 from IET-OU/master

Fixes to "evidence_geomap" PHP, CSS hacks etc...