Persistent instances hash table

Due to the sequential search in the aggregates "model_contents.instances" and actual "enity_extent.instances", a "delete instance" operation may be very slow when the actual model has a large number of instances. Hence for large models with a large number of "delete instance" (model merge) operation should use the EDMpersistentInstancesHashTable to speed up such "delete instance" operations. The EDMpersistenInstancesHashTable must be specified when the actual model is created. Hence, the functionality to specify this concept is available in all "create model" operations. The actual option is named PERSISTENT_INSTANCES_HASH_TABLE.

The functions edmiHashModelInstances() and xpxHashModelInstances() to build a temporary model instances hash table will fail on a model with a EDMpersistentInstancesHashTable.