Adds an Organisation

If you have trouble with creating an Organisation, try creating Organisations via the web interface, and then access those Organisations via the API. This way you can see examples of the fields and sub-elements attached to the Organisation. A common source of problems during write/update request is caused when users omit required fields, or insert invalid data in a field (e.g. reference a CATEGORY_ID that does not exist in the user's Insightly instance.