Added hidden as a type of field

This is for the Local SEO plugin, where the hidden field is needed for the Google Maps custom marker
Added hidden as a type of field

This is for the Local SEO plugin, where the hidden field is needed for the Google Maps custom marker
Merge branch 'master' of github.com:YourMark/wordpress-seo

Conflicts:
	admin/class-taxonomy.php
Added a space before the (
Of course the label needs to be hidden too
Merge pull request #1445 from YourMark/master

Added hidden as a type of field, props @YourMark