Adds a schedule_json view

This is based off of @taavi's pull request, #45, and is also informed from [views.py](https://github.com/pyohio/pyohio/blob/master/pyohio/views.py) in the pyohio/pyohio repo.

Testing: It wasn't clear how to test symposion on its own, and I kludged something together so that I could test this change outside of the context of a conference site. To test the change, make sure that `requirements-test.txt` are installed, then run `./runtests.py` from within the `schedule` app test directory. The `requirements-text.txt`, `factories.py`, `runtests.py`, and `test_views.py` are all related to testing the change. Building up a nice schedule factory is a pain, so I'm stopping now to make this PR to get comments. I'm willing to bet people with more experience than me can provide guidance here.