Refactor of Inheritance and Features

* Removed AS_CURRENCY_BASIS as it was not needed.
* Moved TEST_ASSET_ACCOUNT to a new location.
* Added better class note descriptions as needed.
* AS_ACCOUNT: Refactor of basis.balance to just balance by way of
inheritance change.
* AS_CURRENCY_ACCOUNT: Added default_create to handle creation of
balance.
* AS_BASIS: Basis now has increase and decrease balance function.

NOTE: The `old' keyword does not seem to be working. I will take this up
with Eiffel Software.