feature: add makeh5files_single CLI command to track floes in individual files

[hollandjg]

Add a single-file version of the HDF5 files script.

Call it like this:

${IFT} makeh5files_single --truecolor ${TRUECOLOR} --falsecolor ${FALSECOLOR} --labeled ${SEGMENTED} --props ${FLOEPROPERTIES}

... where ${IFT} is the CLI, ${FLOEPROPERTIES} is the path to the CSV file containing the floe properties, and the other variable names are image files.

Adds:

• New CLI command
• New smoke test

Part of:

• Update Cylc to handle new FSD #149