Added test coverage for topic gathering

Two new tests added to check that scraper works when Topics (Chicago) or Indexes (Philly)
are present and not present for legislation. Despite being called two different things, both sets of topics are held in a <span> with the same ID so the current set up should work and the tests are written to test that.

I guess the  index/topic stuff from @mjumbewu snuck in on the last pull request even though I did that git revert.

Nevertheless - this should complete the topic/index addition to the scraper for Philly and Chicago.