Update BookReference model

Add locale; change sources to object with keys = source and value = id

server/sequelize/models/BookReference.js

@@ -18,8 +18,8 @@ module.exports = sequelize => sequelize.define('BookReference', {
   sources: {
     type: Sequelize.JSON,
     allowNull: false,
-    defaultValue: [],
+    defaultValue: {},
-    comment: 'A JSON array with each element being an object with named source <STRING> and source id <STRING>',
+    comment: 'A JSON object with each key a source name and value a source id',
   },
   covers: {
     type: Sequelize.JSON,
@@ -27,6 +27,12 @@ module.exports = sequelize => sequelize.define('BookReference', {
     defaultValue: [],
     comment: 'A JSON array with each element being an object with image url <STRING> and source id <STRING>',
   },
+  locale: {
+    type: Sequelize.STRING,
+    allowNull: false,
+    defaultValue: 'en',
+    comment: 'A basic locale string',
+  },
 }, {
   timestamps: false,
   indexes: [
@@ -40,5 +46,8 @@ module.exports = sequelize => sequelize.define('BookReference', {
     {
       fields: ['description'],
     },
+    {
+      fields: ['locale'],
+    },
   ],
 });