Fixes for "broken" tag URLs, [hypothesis_summary] shortcode recursion ... [LACE]+

Hi Martin,

When you have a moment would you like to review and merge these changes please? Quite a number  of significant fixes/ enhancements:

* Bug #28, a fix for tag URLs, which appeared to be broken in LACE - [they now contain evidence](http://evidence.laceproject.eu/?tag=ev-evaluation);
* Bug #31/ #33, use of `the_excerpt()` in `[hypothesis_summary]` shortcode can cause recursion when no explicit excerpt is set (shortcodes recursively evaluated) - leading to site crashes(!)
* Bug #29, CSS fix for primary navigation obscured under the  evidence map;
* Bug #30, Re-factoring PHP - an ongoing effort...

Thank you,

Nick