We were very inconsistent regarding these rules.
Personally I prefer no empty lines around blocks, clases, etc... as
recommended by the Ruby style guide [1], and they're the default values
in rubocop, so those are the settings I'm applying.
The exception is the `private` access modifier, since we were leaving
empty lines around it most of the time. That's the default rubocop rule
as well. Personally I don't have a strong preference about this one.
[1] https://rubystyle.guide/#empty-lines-around-bodies
Why:
ValuatorGroup name should be unique and present to be able to identify
correctly each of them.
How:
- Adding a presence & uniqueness validation at the model
- Adding a sequenced value for name attribute at its factory
- Adding missing model spec that covers validations
