Descriptive md

This request included extension for work, copy and file descriptive metadata:
- Description: base class for all descriptive metadata.
- DescriptionOf: the relation to associate a type of descriptive metadata (e.g. Geocoding) to either Work, Copy, etc.

The new APIs made available under this extension are:
- Node: 
    getDescriptions() : return an iterable list of further descriptive metadata (in addition to the base set). (e.g.    
                                  For a work, you can get Geocoding and IPTC as the additions)
    getDescription(String fmt): e.g. If you put “Geocoding” as the fmt, you’ll the geocoding related metadata for 
                                               the node if there’s any.
- Work:
    getGeoCoding(): return the Geo coding associated with this work if there’s any
    addGeoCoding(): associate Geo coding metadata to this work.
    getIPTC(): return the IPTC metadata associated with this work if there’s any
    addIPTC(): associate IPTC metadata to this work.

- Copy:
   getCameraData(): return the Camera data associated with this copy if there’s any
    addCameraData(): associate Camera data to this copy.