move diff script in git/

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
rename the method to get the name of an actor

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
fix "Error, no message..." errors

Link: https://github.com/GeneAssembly/biosal/issues/384
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>