SPIKE: expose test utilities for import into modules.

Currently interactors/test setup methods are only imported via direct file path to `stripes-*/etc/etc....`
This requires a direct devDependecy on the 'stripes-*' module rather than 'stripes' which isn't what we want.
They should not have to reach into the directory structure, but be able to import through stripes (or other easy means)
Test utilities should not end up in the production bundle (filtered out? tree shook?)

An approach might be to set a particular webpack entry point based on a `process.env` variable (test?) in stripes-core