unify calibrate function

With the MM experimental station at SXP, the calibration process, i.e. converting time-of-flight values into energy values, can be done in two different ways:

• Taking a sequence of runs changing some experimental parameters and looking at a particular position, its time-of-flight, to see how this position change. Most of the times it is done following this approach.
• Or by looking at two/three different features in a single run giving the position (in time-of-flight units) of those features.

Depending on the input of the function, either a single energy point or a set of them, it requires different parameters to be passed to the calibration function's signature.

This MR unifies under a single function sxp.calibration.calibrate the conversion between time-of-flight (i.e., what it is recorded by the detector) into energy, a more meaningful value that is independent of the experimental conditions.