Feature/aggregate statistics generator pull request into develop.

Created by: brj496

Merging Feature/aggregate statistics generator. Adds:

• backend/controllers/aggregateStatisticsController.js
• backend/routes/aggregateStatisticsGenerator.js
• backend/helperFiles/artifactsHelper.js
• backend/helperFiles/artifactTypesHelper.js
• backend/helperFiles/cataloguesHelper.js
• backend/helperFiles/projectilePointsHelper.js
• backend/helperFiles/sitesHelper.js
• backend/tests/config/aggregateStatisticsGenerator.test.js

includes changes to the following routes:

• backend/routes/artifacts.js
• backend/routes/artifactTypes.js
• backend/routes/catalogues.js
• backend/routes/projectilePoints.js
• backend/routes/sites.js