LP#1708291: add a egShareDepthSelector directive

LP#1708291: add a egShareDepthSelector directive

This directive implements a selector for OU-sharing depths; depths
and names come from the actor.org_unit_type table. If there are
multiple types defined for a given depth, the display value in
the selector is the concatenation of their names.

The initial use of this directive is for specifying how broadly
prediction pattern templates should be seen.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>