Improve TestLoader to use the Google Sheets API

[andymina]

The test loader, as described in #38, is great, but can ultimately be improved. Currently, to load or update tests, after filling out the correct information in Google Sheets I have to manually download each of the sheets, adjust the sizes of each matrix (if necessary) in the test loader, and then run it to export the new data.json.

While these don't seem like a lot of steps right, most of this process can be automated if I use the Google Sheets API. It might be easier to do this in a language like JavaScript rather than wrestle API requests with C++. Should I come back around to using JS, I might convert the current TestLoader to JS as well.