thorium: use action instead of tag in send functions

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: add functions to send 2 int values

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: move message helpers in thorium

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>