Setup backend testing tools

As a developer I need standard testing tools so that I can practice test driven development without having to worry about setting them up correctly.

Acceptance criteria

[x] It should use rspec and rspec-rails as the main test framework
[x] It should install / use Simplecov
[x] It should install / use FactoryBotRails for fixtures/test data
[x] It should install webmock for mocking HTTP requests / testing external services
[x] It should install shoulda-matchers for testing active-x code