Add task links (Merge pull-request #610)

assets/js/src/link.js

@@ -0,0 +1,19 @@
+Kanboard.Link = (function() {
+
+    function on_change() {
+        if ($('.behaviour').prop('checked')) {
+            $('.link-inverse-label').hide();
+        }
+        else {
+            $('.link-inverse-label').show();
+        }
+    }
+
+    jQuery(document).ready(function() {
+        if (Kanboard.Exists("link-edit-section")) {
+            on_change();
+            $(".behaviour").click(on_change);
+        }
+    });
+
+})();