Issue 1540 - New meta-data custom field type of "link"
    
    Added a new custom field type of "link", that is in addition
    to "boolean" and "text".  Multiple links can be specified by
    separating them with commas.  Then when rendering the the issues
    page, convert the value(s) to a hrefs
    
    Fixes https://pagure.io/pagure/issue/1540