Force forms and fields to use plugin resolution

Instead of using the interface/subinterface code that was currently being implemented for the plugin.
(cherry picked from commit 1467ec7)

sleekxmpp/plugins/xep_0004/stanza/field.py

@@ -13,8 +13,9 @@ class FormField(ElementBase):
     namespace = 'jabber:x:data'
     name = 'field'
     plugin_attrib = 'field'
+    plugin_multi_attrib = 'fields'
     interfaces = set(('answer', 'desc', 'required', 'value',
-                      'options', 'label', 'type', 'var'))
+                      'label', 'type', 'var'))
     sub_interfaces = set(('desc',))
     plugin_tag_map = {}
     plugin_attrib_map = {}
@@ -165,6 +166,7 @@ class FieldOption(ElementBase):
     plugin_attrib = 'option'
     interfaces = set(('label', 'value'))
     sub_interfaces = set(('value',))
+    plugin_multi_attrib = 'options'
 
 
 FormField.addOption = FormField.add_option

sleekxmpp/plugins/xep_0004/stanza/form.py

@@ -22,8 +22,8 @@ class Form(ElementBase):
     namespace = 'jabber:x:data'
     name = 'x'
     plugin_attrib = 'form'
-    interfaces = set(('fields', 'instructions', 'items',
-                      'reported', 'title', 'type', 'values'))
+    interfaces = set(('instructions', 'items',
+                      'reported', 'title', 'type', ))
     sub_interfaces = set(('title',))
     form_types = set(('cancel', 'form', 'result', 'submit'))
 
@@ -48,7 +48,7 @@ class Form(ElementBase):
     def set_type(self, ftype):
         self._set_attr('type', ftype)
         if ftype == 'submit':
-            fields = self['fields']
+            fields = self.get_fields()
             for var in fields:
                 field = fields[var]
                 del field['type']
@@ -74,7 +74,8 @@ class Form(ElementBase):
             field['desc'] = desc
             field['required'] = required
             if options is not None:
-                field['options'] = options
+                for option in options:
+                    field.add_option(**option)
         else:
             del field['type']
         self.append(field)
@@ -227,9 +228,9 @@ class Form(ElementBase):
     def set_values(self, values):
         fields = self['fields']
         for field in values:
-            if field not in fields:
+            if field not in self.get_fields():
                 fields[field] = self.add_field(var=field)
-            fields[field]['value'] = values[field]
+            self.get_fields()[field]['value'] = values[field]
 
     def merge(self, other):
         new = copy.copy(self)