Remove prototype package dependency

[jstotz]

Hi Clover team,

Not sure if you want this PR but because of the reasons described in #16 we
were unable to use the SDK with the prototype package as a dependency.

This change:

• Extracts the Class implementation from the prototype package as a
  standalone file that does not modify any globals (see Class.js).
• Updates README to describe new way of extending classes
• Manually patches the files generated by Avro. If someone wants
  to point me at the code that generates these files from the Avro schemas
  I'd be happy to update that, too.

I've tested this change in our app and it appears to work as expected
but we certainly don't exercise the entire SDK codebase.

Resolves #16

[mike-clover-com]

Hi Jay. Ironic, but you may see that there is another pull request here to remove this dependency - opened shortly after yours.

Please feel free to take a look at the other pull request. It is closely tied to https://github.com/clover/remote-pay-cloud-api, a new repository that breaks out the api classes (and also avoids the prototype.js dependency). There are also three other repositories/pull requests that may be of interest - https://github.com/clover/remote-pay-cloud-connector-configuration-react/pull/7 and https://github.com/clover/clover-cloud-connector-example/pull/7 are an example application, and https://github.com/clover/clover-cloud-connector-unit-examples/pull/4 is another example application that is useful for testing functionality.

I will take a look at your pull request as well, but I think that we may have this resolved shortly - including appropriate NPM publishings, by the end of this week.

[jstotz]

Ha, well that's some timing. Thanks for getting that done. The approach you took in #23 to use plain old constructor functions and prototype manipulation is definitely better. Particularly nice for us since we use ES6 and it's now compatible with class OurListener extends ICloverConnectorListener syntax.

Feel free to close this PR.