Fix imports and fplot.plot for new datatypes
Relocated fit out of datatypes and into curvefit

curvefit.fitWLC(): new function that takes x, f, and mask and
returns a Fit object using MMS by default.

TrapData.maskFromLimits(): _constrainFitFromLimits() function
that now returns index array of data to use.

Pulling.fitForceExtension(): applies data limits, fits, and plots
data using fplot. Called by fitHandles() and fitRip().
Merge branch 'type-refactor' of github.com:cfperez/smbanalyze into type-refactor