Gets the id of a CPO. The id can be set
during construction by a CPOConstructor
using the id parameter, or with setCPOId.
The exported hyperparameters of a CPO all have the id as prefix. This makes it possible to compose CPOs that have clashing parameter names.
getCPOId(cpo)[CPO]
The cpo.
[character(1)] the CPO's id.
Other getters and setters: CPO,
  getCPOAffect, getCPOClass,
  getCPOConstructor,
  getCPOName,
  getCPOOperatingType,
  getCPOPredictType,
  getCPOProperties,
  getCPOTrainedCPO,
  getCPOTrainedCapability,
  setCPOId
Other CPO ID related: setCPOId