Don't try to batch_save calculated attributes.

This results, unsurprisingly, in a lot of 'SettingTotalDirectlyNotSupported' errors.
Merge pull request #100 from fimmtiu/fix-batch-save-attributes

Don't try to batch_save calculated attributes.
Added ShortCode to Organisation model
Merge pull request #104 from mjalvarez/master

Added ShortCode to Organisation model