Add support for adding Client Certificates to access-lists

Client certificate support is added as a new separate type of option for
access-lists.

This commit is the support code to enable access-lists to contain
Client Certificate references.

frontend/js/models/access-list.js

@@ -11,6 +11,7 @@ const model = Backbone.Model.extend({
             name:            '',
             items:           [],
             clients:         [],
+            clientcas:       [],
             // The following are expansions:
             owner:           null
         };