SaveOrder method should throw more meaningful exceptions

In the new Order Entry API, the Order Service API method provides several validation checks--for example, not allowing two active orders for the same orderable and care setting, cannot edit an existing order, etc...

However, in each case a standard OpenMRS API exception is thrown, with the error message hard-coded in English text.

In order to allow consumers of this API to take custom actions on an error, such as displaying a localized error message, the API should throw new, targeted exceptions such as "DuplicateActiveOrder" that extend APIException.

burke darius Thoughts?