Define "RawEventData" and "UDD" models

[drbenmorgan]

The input of this program will be the "RawTriggerData" model, which will handled in the SuperNEMO-DBD/SNRawDataProducts project. The primary output will be "RawEventData", and we know that downstream of this there may be an additional and as yet undefined "UDD" data model.

"RED/UDD" will be the primary input data to the calibration stage, so this project should take responsibility for:

1. Defining and producing code for the "RawEventData" classes
2. Defining and producing code for the "UDD" model
3. Outlining the process of how "RED" is transformed to "UDD"

Keeping everything together at the start will keep things simple, and we can then split out data models/libraries as use cases become clearer.