Retrofit the Drip #track method and add #identify support

We recently made some changes/enhancements to our JavaScript API:
https://www.getdrip.com/docs/js-api

Namely, we changed the argument structure of our `#track` method to more closely follow standard patterns (although we are maintaining backwards compatibility) and we added support for the `#identify` method. These changes are reflected here.

**Note**: I think my tests are correct, but I cannot seem to get the test suite to pass. I'm getting this error all over the place. Any guidance on this?

```
Error: Don't override the "loaded" method from the base integration
      at :19
      at Tester (:71)
      at Tester (:57)
      at http://localhost:4202/test/integrations/drip.js:118
      at http://localhost:4202/test/mocha.js:4212
      at http://localhost:4202/test/mocha.js:4584
      at http://localhost:4202/test/mocha.js:4643
      at next (http://localhost:4202/test/mocha.js:4510)
      at http://localhost:4202/test/mocha.js:4519
      at next (http://localhost:4202/test/mocha.js:4463)
      at http://localhost:4202/test/mocha.js:4482
      at http://localhost:4202/test/mocha.js:4214
      at next (http://localhost:4202/test/mocha.js:4483)
      at http://localhost:4202/test/mocha.js:4487
      at timeslice (http://localhost:4202/test/mocha.js:5480)
```