refactor the notion of a session

This is essentially an undo of the work that resulted in the user-managed
Session objects.  The concept of a session now corresponds to the lifecycle
of EntityStore instances (this is more in-line with JPA).
implement an EntityStoreFactory
remove cached entry when deleting persisted object
remove unused exception
saner creation of new instances
project name is Lucidity
wrap Cassandra driver exceptions
update instance cache when peristing object update
drop javax.persistence annotations in favor of our own

The annotation names/meanings remain the same, but the local copies
only accept arguments we support; Should better drive home the point
that this is not JPA, and JPA semantics are not supported.
(again )change the package space