visitor: use ACTION_ASSEMBLY_GET_VERTEX_AND_SET_VISITOR_FLAG on main vertex

Link: https://github.com/GeneAssembly/biosal/issues/836
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
assembly_graph_store: set flag when action is ACTION_ASSEMBLY_GET_VERTEX_AND_SET_VISITOR_FLAG

Link: https://github.com/GeneAssembly/biosal/issues/836
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
visitor: add some code to increase data locality

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

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

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