Fixed abtests to use the preferences scope correctly.

Made abtests display its children in the right order.

common/lib/xmodule/xmodule/abtest_module.py

@@ -129,7 +129,9 @@ class ABTestDescriptor(ABTestFields, RawDescriptor, XmlDescriptor):
             raise InvalidDefinitionError("ABTest portions must add up to less than or equal to 1")
 
         group_portions[DEFAULT] = default_portion
-        children.sort()
+        # I have no clue why the line of code below ever existed.
+        # It was scrambling the order of all the elements in abtest.
+        # children.sort()
 
         return {
             'group_portions': group_portions,