Adding new Attribute Interfaces to java-api.

[Rod Widdowson]

I'm intending following Scott's lead and adding Interfaces in front of the
major attribute functionality

- AttributeFilter
- AttributeDefinition
- DataConnectorDefinition
- AttributeResolver

(Attribute mapping is already behind an interface)

In most cases the Interface would collect most of the methods and inherit
the name currently used by the definition.  The definition would then become
BaseXXXX (or, if not abstract ConcreteXXX - unless anyone has a better name
for this case)

The motivation is to provide another, very high level plugin point for
people who need that level of control.  I'm just firing a mail in here to
test whether anyone thinks this is a bad idea and to ask whether anyone has
a preference for whether the interfaces should go in idp-attribute-api, or
into the appropriate idp-attribute-*-api module?

Rod