Export to CSV file in a headless mode

[tinevez]

The CSV export methods in the table classes only exports what is directly shown in the tables, and use the GUI classes of Java. This causes errors when used in a script in a headless model. See the discussion:

https://forum.image.sc/t/error-headlessexception-when-trying-to-save-csv-file-of-tracking-data-from-trackmate-when-running-headlessly/94304/5

This commit adds a utility that exports the content of a model in a headless mode.

This:

CSVExporter.exportSpots( 'trackmate-output.csv', trackmate_model, False );

results in: