BiggyList Json Tests

Some initial tests for JSON persistence. In an attempt to use more diverse data than the values I could contrive, I'm using generated JSON files from http://www.json-generator.com/. These files are somewhat large and rather than bloat future git clone operations with bogus test data I've hosted them on dropbox and the test pull them down when missing.

Ideally I'd like to have Low, Medium and High test filters that choose the corresponding sample data file based on the testing goals of the user but I haven't found a good way to do that with xunit yet beyond moving the tests into separate test classes with unique trait values. For the time being the larger tests are commented out (and I haven't added much coverage yet) and I could revert or remove them based on feedback as to whether or not this aspect is warranted.