Adjustments to interfaces to improve the mockability and faking of NATS for unit testing in consumer apps.

[sspates]

Updated a few interfaces to use IConnection instead of Connection as Connection is internal. This is preventing mocking libraries from being able to mock properly.
Added interface for ConnectionFactory so factory can be mocked/faked in unit tests.

[scottf]

I like this idea but we cannot change the interface in a non backward compatible way.

[sspates]

@scottf I removed the IConnection changes, but found that protecting the Message in the handler makes mocking the handling of the message impossible. I adjusted the Handler to expose the message to being set.

[scottf]

@sspates-starbucks I'm good with the event message changes, not excited about having a public setter, but I suppose it's benign, the worst that could happen is the dev overwrites their own message.
Frankly I'm not seeing the need for the IConnectionFactory interface. There is already an IConnection interface so you can provide your own mock connection if you want to.
And I'll mention again the ability to run a server locally during tests. In .net integration tests we generally start a server for each suite, but for java we start a server for each test.

[scottf]

LGTM