Add Registrant API contact update action

Closes #849

db/migrate/20180824215326_create_actions.rb

@@ -0,0 +1,9 @@
+class CreateActions < ActiveRecord::Migration
+  def change
+    create_table :actions do |t|
+      t.belongs_to :user, foreign_key: true
+      t.string :operation
+      t.datetime :created_at
+    end
+  end
+end

db/migrate/20180825193437_change_actions_operation_to_not_null.rb

@@ -0,0 +1,5 @@
+class ChangeActionsOperationToNotNull < ActiveRecord::Migration
+  def change
+    change_column_null :actions, :operation, false
+  end
+end

db/migrate/20180825232819_add_contact_id_to_actions.rb

@@ -0,0 +1,5 @@
+class AddContactIdToActions < ActiveRecord::Migration
+  def change
+    add_reference :actions, :contact, foreign_key: true
+  end
+end

db/migrate/20180826162821_add_action_id_to_notifications.rb

@@ -0,0 +1,5 @@
+class AddActionIdToNotifications < ActiveRecord::Migration
+  def change
+    add_reference :notifications, :action, foreign_key: true
+  end
+end