Adds or updates an item within local storage. 
      writeItem( type, handle, data, onSuccess, onFailure )
    
This method does not return anything.
          | Name | Description | Type | Use | 
          | type | Denotes the type of data to be written. Item types are freely defined data item
            categories. | string | required | 
          | handle | Data item identifier. Supports partial matches if full matches are not found. | string | required | 
          | data | The updated data item's data string. | string | required | 
          | onSuccess | A callback function, informs that the operation completed successfully. | function | required | 
          | onFailure | A callback function, called when the operation fails. Passes an error code, as defined
            in the Constants table in the Client Store article, and an error message. | function | required |