Adds NXexperiment and NXmeasurement

[domna]

@lukaspie @mkuehbach @RubelMozumder @sherjeelshabih @sanbrock
This is a general experiment and measurement, which I drafted some time ago. Maybe this comes in handy when we build the experiment recipe for #52 . NXmeasurement, is, however, just a collection of thoughts and no valid (n)yaml file, yet.

[lukaspie]

How would NXexperiment be used? Would our appdefs, e.g. NXmpes, extend NXexperiment? I guess the experiment recipe (at least what I was imagining) is given by NXmeasurement and not really by NXexperiment.

[domna]

How would NXexperiment be used? Would our appdefs, e.g. NXmpes, extend NXexperiment? I guess the experiment recipe (at least what I was imagining) is given by NXmeasurement and not really by NXexperiment.

Yes, this was the idea to have a general NXexperiment to be inherited from in all appdefs to have a general agreed structure.
You are right the recipe is only given by NXmeasurement. I just pushed this here because I had both and used NXmeasurement in NXexperiment, so I thought it's most convenient to have them here together. But we can also separate the NXmeasurement (but this needs some work and polish anyways - just a rough draft).