Improve continuous integration testing

[ajmedford]

The infrastructure for Travis CI testing has been added, and a very crude testing system which runs the tutorials and ensures that there are no crashes at each commit. However, this could be significantly improved by:

1. streamlining the testing process to run a single script which automatically looks for new tutorials, etc.
2. checking that the output of the tutorials matches what is expected, in addition to ensuring that they do not crash
3. adding more tests. In general there should be some standards for developers who add new functionality to create a test/tutorial that ensures their new function does not get broken in future commits.