code: function flattenMessageMap(data) {
      var obj = {};
      var newKey;
  
      _.each(data, function(groupMessages, key) {
          _.each(groupMessages, function(message, subKey) {
              newKey = [key, subKey].join('.');
              obj[newKey] = message;
          });
      }, this);
  
      return obj;
  }
docs: Flatten message map
  @param {object} data - Messages
  @returns {object} Flatten message object (key foramt is 'key.subKey')
  @ignore