Unique IDs in workspaces

[piotras]

Currently, we use object's ID as additional workspace ID identifier. It should be implemented so other unique ID could be used to avoid additional select after object is created. This could help us with transaction isolation level.

Basically, we must get rid of this:

query = g_string_new ("UPDATE ");
g_string_append_printf (query, " %s SET %s=%d WHERE id=%d",
tablename, MGD_WORKSPACE_OID_FIELD, new_id, new_id);
midgard_core_query_execute(MGD_OBJECT_CNC (object), query->str, FALSE);