thorium: add action ACTION_ENABLE_VERBOSE_MODE

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
unitig_visitor: add support for ACTION_ENABLE_VERBOSE_MODE

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
unitigs: reduce verbosity in the visitor code

Link: https://github.com/GeneAssembly/biosal/issues/799
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>