Bug #18, Fix to safely get json-decoded properties [LACE]

* .. From within WordPress post description
* WP shortcode:  [evidence_summary]
* New PHP method: Evidence_Hub_Shortcode_Evidence_Summary::json_get()
* Evidence_Hub_Shortcode::debug()
Fix to "sankey-main" Javascript - hide the "Loading" message on success

* WP shortcode:  `[hypothesis_sankey]`
JSLint fixes to sankey-main Javascript
Merge branch 'master' of github.com:IET-OU/wp-evidence-hub
Bug #20, Fix - Skeleton's `.clear` makes WordPress footer disappear!

* Pull #18
Merge pull request #19 from IET-OU/master

Bug #18, Fix to safely get json-decoded properties [LACE]