Create shortcut for BaseService-related imports (#2809)

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.

services/pub/pub.tester.js

@@ -1,11 +1,10 @@
 'use strict'
 
 const Joi = require('joi')
-const ServiceTester = require('../service-tester')
+const { ServiceTester } = require('..')
 const { isVPlusTripleDottedVersion } = require('../test-validators')
 
-const t = new ServiceTester({ id: 'pub', title: 'Pub' })
-module.exports = t
+const t = (module.exports = new ServiceTester({ id: 'pub', title: 'Pub' }))
 
 t.create('package version')
   .get('/v/box2d.json')