add stubbed out mobject-store source with notes

src/mobject-store.c

+/*
+ * (C) 2017 The University of Chicago
+ * 
+ * See COPYRIGHT in top-level directory.
+ */
+
+#include <margo.h>
+#include <ssg.h>
+
+#include "mobject-store.h"
+
+struct mobject_store_handle
+{
+
+};
+
+const char *mobject_global_pool = "mobject-global-pool";
+
+int mobject_store_create(mobject_store_t *cluster)
+{
+    /* XXX alloc, set handle */
+
+    /* XXX find the SSG group ID for the mobject cluster group */
+}
+
+int mobject_store_connect(mobject_store_t cluster)
+{
+    /* XXX ssg attach to mobject cluster group id */
+}
+
+int mobject_store_shutdown(mobject_store_t cluster)
+{
+    /* XXX ssg detatch from mobject cluster group id */
+
+    /* XXX free handle */
+}
+