FormatTools: rename some calibrate methods

These methods actually created new CalibratedAxis objects from
AxisTypes, so are better named createAxis/createAxes.

The remaining "calibrate" methods actually do assign calibration if the
relevant CalibratedAxis objects in fact implement LinearAxis (which they
will if created using createAxis or createAxes).
FormatTools: add getScale convenience method

This method uses the CalibratedAxis#averageScale(int, int) method to
return the average scale over the length of the axis. For linear axes
(which will be by far the most common), this will simply be the slope of
the axis (i.e., its "calibration value"). However, for nonlinear axes
this will average the scale over the axis, which is better than nothing.