Add calibration to Marching cubes mesh

[rimadoma]

Adds an optional parameter to add calibration to the output mesh of DefaultMarchingCubes, as discussed on the forum

Couple of questions remaining:

1. Should the op consider different units for different axes? How would that work? Convert all to unit of x-axis and scale with that?
2. Is it possible to have a @Parameter CalibratedAxis[] axes? I'm getting "last argument should be vararg" errors from namespace tests.
3. Would it make sense to have a CalibratedMarchingCubes op that takes in an ImgPlus<T>?

[kephale]

This should be accounted for in imagej-mesh: imagej/imagej-mesh#22

[frauzufall]

@rimadoma just a note, @tpietzsch and I have been working on significantly speeding up DefaultMarchingCubes on this branch. The branch is just a playground, I want to add add the new versions to imagej-mesh as static methods and call this from ops. I will ping you once there is a PR so that we can also address this issue.