Migrate tests to jest

[nason]

This is a rather large PR but I refactored the tests to use jest, and in doing so:

• removed the dependency on nock in tests
• organized tests into separate files, co-located with source
• leveraged snapshot testing heavily
• removed ~600 lines of test code
• abstracted away some repetitiveness to make it easier to add test cases
• in addition to src, run against es build (TODO figure out running against lib build too)

[coveralls]

Coverage remained the same at 100.0% when pulling 4532813 on test-w-jest into 1ed4ab0 on next.

[nason]

Unrelated -- but I want to note that there are still a few situations in which REQUEST and SUCCESS type actions dispatch with an error flag

I think a follow up to #175 is in order