Module-specific options
https://gitlab.science.ru.nl/clean-and-itasks/clean-platform/merge_requests/266 adds some tests for Text.Encoding.Base64. Because Platform tests with Tests 100000 and these are quite heavy, testing takes a long time, while this many tests is not actually needed for that module. But to set options for different modules from the command-line would get very complicated very quickly. Perhaps we can add a .testproperties.json configuration file where both the defaults and per-module overrides are stored.