Fixes #19781 - Fix Layout/LeadingCommentSpace cop

Fixes #19787 - Fix Layout/SpaceAfterComma cop

Fixes #18718 - Empty boolean matcher should not turn into false

fixes #16557 - move tests into modern Rails layout

Models, controllers, mailers and helpers are now in test/ subdirs
matching app/ subdirs. Service, miscellaneous and old test/lib/ tests
are now in test/unit/ separated from models, which obsoletes the custom...

Fixes #3582 - Parameters on subnets

Fixes #11618 - Replace validation tests by shoulda-matchers

A good chunk of our unit tests are testing whether a validation is
working or not by testing it actively. For the validations we've
added ourselves I would say it's fine. However for validations that...