actor destructor and constructor are now called from node

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
set thread to NULL in actor constructor

Link: https://github.com/GeneAssembly/biosal/issues/31
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
add mutex in notify_death

Link: https://github.com/GeneAssembly/biosal/issues/30
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
remove states in bsal_work

Link: https://github.com/GeneAssembly/biosal/issues/22
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
add calls to select threads for dispatching

Link: https://github.com/GeneAssembly/biosal/issues/1
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>