Fixes#2876 with @paulmelnikow's suggestion
Moved imports of `ServiceTester` and `createServiceTester` to a separate file so that dev dependencies are not imported by service classes.
Continue to implement #2698:
- Add `core/base-service/index.js` (but hold off on moving the things it imports)
- Add shortcuts in `services/index.js` for Base*Service, errors, and deprecatedService. This file will be streamlined later to avoid cluttering it with rarely used bits.
- Apply consistent ordering of imports and use of `module.exports` in testers.
- Remove some renaming of imports.
- Remove obsolete tests here and there.
Numeric colors weren't properly being handled by `makeBadge` after #2742.
Since this function really does not need to be accepting colors as strings, rather than make the function more lenient to work with Scoutcamp, I coerced the types of the colors on the way in.
Two tests cover the functionality in the modern service. I don't feel strongly that the legacy version needs coverage at this point, though I've added one for the moment on the github languages badge where this manifested.
Fix#2778
