Integration of structured gettables in the measurement control. decouple responsibilities in the acquisition loop.

Relates to quantify-core#343 (moved) and quantify-core#301

This issue is about adding support for the structured Gettable of quantify-core#343 (moved) to MeasurementControl.

The MeasurementControl is currently responsible for all the data reshaping and combines a bit too much custom functionality in one step. The proposed solution is to refactor the measurement control such that

• there is one step responsible for executing a single iteration of an experiment. This step calls settables and gettables and returns the combined xarray dataset.
• there is a separate step responsible for storing the data/writing to disk (quantify-core#301 )
• there is a separate step responsible for broadcasting that there is new data to a plotmon/other watching services.