Add global settings base class [SCI-1004]

app/models/settings.rb

@@ -0,0 +1,3 @@
+class Settings < ActiveRecord::Base
+  private_class_method :new
+end

db/migrate/20170217141402_create_settings_table.rb

@@ -0,0 +1,9 @@
+class CreateSettingsTable < ActiveRecord::Migration
+  def change
+    create_table :settings do |t|
+      t.text :type, null: false
+      t.jsonb :values, null: false, default: '{}'
+    end
+    add_index(:settings, :type, unique: true)
+  end
+end