disambiguate class names `InstrumentEditController` and `InstrumentsEditController`

We have source pairs

• GUI/Model/Device/InstrumentsEditController,
• GUI/View/Instrument/InstrumentEditController. The classes defined in these files have almost the same name, except for singular/plural "Instrument" without/with s.

This is confusing at first, and requires extra concentration in perpetuity.

Furthermore: Is a controller a model or a view? It can not be both.

Proposals for better names?

By the way, class InstrumentsEditController has a member InstrumentModel* m_instruments. Why has the member variable a plural name while pointing to a class that has a singular name?