Cities demo exploration not supported in upcoming answer groups rule structure

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Trying to load the cities demo exploration from the admin panel.
OR
2. Trying to test the cities demo exploration in 
exp_services_test.LoadingAndDeletionOfDemosTest.

What is the expected output? What do you see instead?
cities.yaml should be loadable and testable in Oppia. Instead, the new answer 
groups rule structure in the backend eliminated the subject key from rule 
specs, which means the cities exploration no longer works as expected (it was 
the only exploration that used rules with subjects other than answer).

This issue is fixable by upgrading the parameters to support tables and table 
indexing. This will allow the generated cities.yaml file to be recreated 
through the editor with just a few generic states, eliminating the need for the 
complex subject targeting the rules were previously doing.

Original issue reported on code.google.com by bhenn...@google.com on 18 Jun 2015 at 7:04