Decide how to handle the test plugins in core package

[smarlowucf]

Decide how to handle the test plugins in core package

[smarlowucf]

See #60 for context on this issue.

[smarlowucf]

I think what's left here is drop pm.register(local_csp) from initialization code.

[rtamalin]

I think functionally we have completed this task, but I still think we should move the 4 testing support plugins into a subpackage, e.g. testing, under the csp_billing_adapter package, to make it clear that they are not part of the core functionality.

[rtamalin]

I think that all the changes we need for June are in place now, so we can either lose this one as complete, or remove the June and add the July label to reflect that we don't need to complete restructuring right now?

[smarlowucf]

Yeah, closing is fine. A new bug can be opened if we decide to move the modules later.