Don't use `find_by` in scopes
Don't use `find_by` in scopes

As the Rails guides say:

> All scope methods will return an ActiveRecord::Relation object

That means `find_by_kind` will return a relation when nothing is found;
the expected behaviour is to return `nil`, like all `find_by` methods
do.

Using scopes also means strange things happen when we try to chain
scopes like `phases.published.drafting`. With scopes, the `drafting`
part would be ignored and all published phases would be returned.

AyuntamientoMadrid/consul,AyuntamientoMadrid/consul,AyuntamientoMadrid/consul,AyuntamientoMadrid/consul