Joining the translations table caused duplicate records to appear.
Ordering with SQL is simply too hard because we need to consider
fallback locales.
Thanks Senén for providing most of the tests in the poll spec.
Slugs should only be updated on certain conditions, we need a trait that
meets that conditions and the name of the trait passed as a mandatory &
named argument on the sluggable concern
Why:
* Slug must be unique among:
1. Budget slug: among other budgets
2. Group slug: among other groups from its budget
3. Heading slug: among other headings from all the groups from its budget
How:
* Adding checks for all possible scenarios on each model specs
Why:
* Those classes have a slug attribute that needs to be filled
How:
* Just adding the shared example to Budget model spec, and creating the model spec file for Heading and Group to include it as well
