ImgOpenerTest: use new axis API

We stop using the deprecated calibration(int) and instead use the
shiny new averageScale(int) which amounts to the same thing here.
ImgSaver: remove obsolete calibration logic

Against the latest ImgLib2 API, the logic is now tautological, since the
deprecated ImgPlus#calibration(int) method ends up delegating to the
relevant constituent CalibratedAxis's averageScale method anyway.

So there should be no need to do this at all anymore.
ImgSaver: tweak style of if statement
FormatTools: stop using deprecated class
Fix up axis API and variable references

Mostly for historical reasons, there was substantial conflation between
CalibratedAxis and AxisType. We now refer to CalibratedAxis objects as
'axis', and arrays/collections of them as 'axes'. We refer to AxisType
objects as 'axisType', and arrays/collections of them as 'axisTypes'.
The API of various interfaces has also been standardized to use the same
nomenclature based on which arguments it takes and what it really does.
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.
Merge branch 'nonlinear-goodies'

Updates Imglib2 use to the latest CalibratedAxis API. Also has some friendlier
renaming for various Axis-related fields.