Allow orphans and add RefrigerationSystem unit tests

Orphans live!!
The refrigeraion system allows orphaned objects and it is up to the UI
or API user to remove orphaned objects from the model.

Added unit testing to RefrigerationSystem.

Due to unit testing, cleaned up some functionality in
RefrigerationSystem.

CompressorList and RefrigerationCaseAndWalkinList are created in CTOR
(the ModelObjectList)