Allow cascade delete Unit/Quantity

Closes #32

app/models/unit.rb

@@ -3,7 +3,8 @@ class Unit < ApplicationRecord
 
   belongs_to :user, optional: true
   belongs_to :base, optional: true, class_name: "Unit"
-  has_many :subunits, class_name: "Unit", inverse_of: :base, dependent: :restrict_with_error
+  has_many :subunits, class_name: "Unit", inverse_of: :base,
+    dependent: :restrict_with_error
 
   validate if: ->{ base.present? } do
     errors.add(:base, :user_mismatch) unless user_id == base.user_id

app/models/user.rb

@@ -12,10 +12,10 @@ class User < ApplicationRecord
     disabled: 0,    # administratively disallowed to sign in
   }, default: :active, validate: true
 
-  has_many :readouts, dependent: :destroy
+  has_many :readouts, dependent: :delete_all
   accepts_nested_attributes_for :readouts
-  has_many :quantities, dependent: :destroy
-  has_many :units, dependent: :destroy
+  has_many :quantities, dependent: :delete_all
+  has_many :units, dependent: :delete_all
 
   validates :email, presence: true, uniqueness: true,
     length: {maximum: type_for_attribute(:email).limit}