[WIP] Spectroscopy and calibrations integration V1

[eggerdj]

Summary

This is a WIP PR to show and discuss how spectroscopy and calibrations can be integrated through the BackendCalibrations class. See an alternative here: #79.

Details and comments

The spectroscopy experiment is integrated with the calibrations through the BackendCalibrations class. The user will execute the following code:

calibrations = BackendCalibrations(qubit)
...
calibrations.qubit_spectroscopy(qubit=5, force_update=True, group="my_group", experiment_options={"amp": 0.2})

The pros of this integration are:

• The user does not need to write much code.
• The analysis class of spectroscopy is not changed.

The cons of this integrations are:

• The BackendCalibrations will contain a function for each calibration experiment that we will support and may become large.

[yaelbh]

If we go on a dedicated function, then there are three options:

1. qubit_spectroscopy as a method of calibrations (this PR).
2. Same method but outside of the calibrations class, not belonging to any class, but written in some utils file.
3. A composite experiment (overkill).

All these three options share the same pros and cons as written above. There is an additional con (also shared by all of them): although the user enjoys the benefit of not writing a lot of code, she will also suffer from the large number of different functions. She will have to understand which functions exist, what exactly they do, how to use them, what are the differences between them. So a large number of functions to maintain can be a headache not only to developers, but also to users.

[eggerdj]

Closed by #88