Make "detectors" generic to "instruments"

[nmaytan]

In speaking with Bruce, he shared an opinion that assets directories are needed for more than just detectors, i.e. other kinds of instruments that aren't considered to be detectors. This opinion is consistent with the motivation of assets, we just didn't spend a lot of time thinking about the name used in the backend.

The mechanism is sufficient to create whatever arbitrary instrument directories as-is, of course, but it might better to reflect the intended usage throughout the API and database layers.

[nmaytan]

I realized this awkwardly conflicts with the fact that beamlines are called "instruments" as well. Perhaps a more specific name like beamline_daq_instrument would be better.

[stuartcampbell]

If we feel brave we could refactor instruments -> beamlines

[nmaytan]

I'm rather partial to that suggestion, calling them "instruments" is unusual to me. Would this make us inconsistent with PASS?... (and do I care? :p)