Dynamic topology phase 2 (#476)

* IOSS: Add broker class to dynamic topology

The original philosophy of one observer per region is still maintained
with the observers that represent the same FEM model being grouped
together. This means that topology changes on one observer is
propagated to others in the same group

* Add missing serialization calls.

* Fix thread-safety issues

---------

Co-authored-by: Greg Sjaardema <gsjaardema@gmail.com>

packages/seacas/libraries/ioss/src/Ioss_DatabaseIO.h

@@ -285,6 +285,18 @@ namespace Ioss {
       return open_root_group_nl();
     }
 
+    int num_child_group()
+    {
+      IOSS_FUNC_ENTER(m_);
+      return num_child_group_nl();
+    }
+
+    bool open_child_group(int index)
+    {
+      IOSS_FUNC_ENTER(m_);
+      return open_child_group_nl(index);
+    }
+
     Ioss::NameList groups_describe(bool return_full_names = false)
     {
       IOSS_FUNC_ENTER(m_);
@@ -778,6 +790,8 @@ namespace Ioss {
       return elemMap.global_to_local(global);
     }
 
+    virtual int  num_child_group_nl() { return 0; }
+    virtual bool open_child_group_nl(int /* index */) { return false; }
     virtual bool open_root_group_nl() { return false; }
     virtual bool open_group_nl(const std::string & /* group_name */) { return false; }
     virtual bool create_subgroup_nl(const std::string & /* group_name */) { return false; }