Add tests / test coverage tool

# What's New?

 * Got the test suite working (it still fails- but they are legitimate "wrong behavior" failure now I think)
 * Add `SimpleCov`, which will create a text coverage % report after each test is run. You can view it at `farmbot-raspberry-pi-controller/coverage/index.html` after running `rake test`
 * Fixed a small typo in `DBAccess`

Let me know if you have any other issues

# Word of Caution

It looks like environments are not properly set up. For now, I just **configured the test suite to use the development database**. It did not want to load the `:test` env for some reason.