Fake: add labelPlanes option to add human-readable labels to planes

[melissalinkert]

Discussed with @sbesson that in the same line as MakeTestOmeTiff, it might be useful for some test scenarios to have FakeReader show readable ZCT indexes and other metadata included in each plane's pixels. This is encoded already in the "special pixels" in the top left corner, but human-readable values would be nice as well.

showinf test&labelPlanes=true&...fake should draw the relevant metadata in white, as MakeTestOmeTiff does. This doesn't attempt to wrap the image name if it spans multiple lines. The default behavior without the labelPlanes key should remain unchanged.

[sbesson]

Tested with a few example of synthetic images e.g.

% ./tools/showinf "test&labelPlanes=true&sizeZ=20&sizeC=3&sizeT=3&series=2.fake" -series 1

The primary goal from my side was to simplify the validation of plane reading in the context of glencoesoftware/omero-zarr-pixel-buffer#28. Coupled with bioformats2raw, I think this change is sufficient to easy generate test datasets with various modalities and dimensionalities.

Proposing to merge unless @jburel @dominikl can think of features introduced in their investigation worth bringing here.