introducing dataclass to represent listener

[jonbarker68]

Introducing a Listener dataclass

A listener data class which stores an id and an audiogram for the left and right ear will allow us to simplify recipe code and reduce duplication.

• The class can validate that the left and right ear have audiogram measured at the same frequencies
• It can handle the reading of listener data from the standard clarity metadata files
• It will serve as a useful way to pass parameters to functions that expect left and right ear measurements.