This pull request closes#2551: making sure that the keywords don't already appear in the example's title.
I also added validation that checks that they are at least two characters long, as this is enforced by the homepage when type your search.
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.
