First commit of dataset.py
New classes in utils/dataset.py
Added sweep_names method to utils.dataset.py
Updates to dataset and fitting code.

Generic Khalil model fitting now fits a line to the unwrapped phase.
Added functions to calculate the coupling coefficient \chi_c.
Resonator now incorporates a mask so that glitches and other
resonators can be excluded from the fit. Dataset.Fine can now
automatically fit all subsweeps using naive deglitching that seems to
work well.
Merge branch 'dataset'