Full support of ENUM data type

[mkrebs81]

SGr enums are dynamic data types, not static Python enums.

They are defined in EIDs with literal string values and integer ordinal values.

[mkrebs81]

Current implementation (0.5.x) externally supports enums in form of string or integer.

Limitations:

• no specific data type or container for enum values
• conversion between device data type and data point data type may be required