Folder structure for mocks and testing utils #276

A structure of different type of files both shared within testing-utils and only within a package will be established.

This issue is a part of #145

Implementation details

• Every package will have a mocks folder which will include fixtures for data and utils folders for testing utilities that are specific for the package.
• The testing-utils library will include fixtures and utils folders for reusable testing utilities.
• A tsconfig.test file will be created in every package to ignore the contents of the mocks folder.