Input validation for class properties and ZProperties

[j053ph4]

• Partially addresses ZPS-1725, ZPS-481
• In addition to validating for quality control, changes can be leveraged for improved change auditing as well as for expanded data type support
• Added Property class to handle input validation and defaults for supported ClassProperty/ZProperty values
• Updated ClassPropertySpec and ZPropertySpec to perform input validation
• Added support for DateTime class, including constructor/representers for YAML Dumper/Loader classes
• Renamed unit test test_zprop_types.py to test_property_types.py
• Expanded unit test to cover both specified and default property types/values, and testing both ZPropertySpec and ClassPropertySpec examples

[csmouse]

PR has aged out. Closing.