Add new infrastructure to support greater use of __slots__

Add new infrastructure to support greater use of __slots__

* Changed AliasedInsp to use __slots__
* Migrated all of strategy_options to use __slots__ for objects.
  Adds new infrastructure to traversals to support shallow
  copy, to dict and from dict based on internal traversal
  attributes.  Load / _LoadElement then leverage this to
  provide clone / generative / getstate without the need
  for __dict__ or explicit attribute lists.

Doing this change revealed that there are lots of things that
trigger off of whether or not a class has a __visit_name__ attribute.
so to suit that we've gone back to having Visitable, which is
a better name than Traversible at this point  (I think
Traversible is mis-spelled too).

Change-Id: I13d04e494339fac9dbda0b8e78153418abebaf72
References: #7527