Removed memoization of handles

Removed memoization in the handle method
in order to have the Entity and its handle
synchronized.

The corrections in the specs are made,
because the object_id of the Entity
handles are no longer equal and therefore
need an attribute to compare with.
Removed handle instance variable memoization reset

There is no need to reset the memoization/cache
now that the @handle is not memoized in the
handle method.