better segregation of internal and api model.Model

[trolldbois]

potentially we would be able to reset the ProcessContext and its model whereas we probably don't want to touch the internal model used for heapwalker. there should probably be a distinction between the '_internal' Model for allocators modules and the 'user' Model for the search and reverse API

ergo , the "memory_handler.get_model()" should return an empty user version. and a hidden "memory_handler.__get_model()" should return the model loaded with allocators modules.

[trolldbois]

We do want to do that because there is no other way to ensure the heapwalker haystack modules will not be subverted by some weird buggy user code reimporting the haystack modules.