This enables following cops:
Check for useless access modifiers
Lint/UselessAccessModifier
Checks for attempts to use `private` or `protected` to set the
visibility of a class method, which does not work.
Lint/IneffectiveAccessModifier
This also disables two false possitives in concerns.
This adds a ability to use multiple different authentication token
fields in other models. From now on it is necessary to add
authentication token field manually in each class that implements this
mixin.
