webui: add filter to attributes widget

Adds filter field to attribute box in permissions for better user
experience. User can then quickly find the desired attribute.

Initial version of the patch authored by: Adam Misnyovszki

https://fedorahosted.org/freeipa/ticket/4253

Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>

ipalib/plugins/internal.py

@@ -518,6 +518,7 @@ class i18n_messages(Command):
                 "enable": "Enable token",
             },
             "permission": {
+                "filter": _("Filter"),
                 "identity": _("Permission settings"),
                 "managed": _("Attribute breakdown"),
                 "target": _("Target"),