Support scheme-specific rules for mapping notation to URI

[nichtich]

Some vocabularies have specific rules and exceptions how to map a local concept identifier (stored in JSKOS as notation) to a concept URI. The mapping is implemented in class ConceptScheme with two methods notationFromUri and uriFromNotation (the methods conceptFromUri and conceptFromNotation internally use the former methods so they don't need to be modified).

Examples:

• DDC T1--0701-0709 = http://dewey.info/class/1--0701-0709/e23/ :

The mapping may not always be reversible, especially uriFromNotation but this requires more examples.

Solutions:

• hard-code exceptions as part of the class ConceptScheme
• Allow applications to provide custom mapping function(s) for notationFromUri / uriFromNotation.

By the way: in some schemes the notation is not reflected in the URI anyway.