add ability for FGDC <-> ISO transforms

[tomkralidis]

When inserting an FGDC document, GetRecords responses return with the following behaviour:

To reproduce:

• go to ​http://host:port/geonetwork/srv/en/test.csw
• insert an FGDC document (copy/paste ​http://pastebin.com/8PdfSbXt)
• click 'Log in and send request (POST)'
• note the resulting ID (GN resets this per my previous email)

The document is in GN CSW. Now:

• search with outputSchema=http://www.opengis.net/cat/csw/2.0.2 (​http://pastebin.com/NBhYzxsP)
  • see FGDC formatted records returned
• search with outputSchema=http://www.isotc211.org/2005/gmd (​http://pastebin.com/s9tyCkez)
  • see ows:ExceptionReport

Propose to implement finer grained CSW support of FGDC CSDGM with the following capabilities:

• add FGDC as a typeName (fgdc:metadata), with the ability to query against this typeName
• add FGDC as an outputSchema (http://www.opengis.net/cat/csw/csdgm), with the ability to return any record in this outputSchema
• support metadata/idinfo/datasetid (if it exists) as a means to preserve the identifier (else autogenerate UUID)

[tomkralidis]

Note: FYI this will require metadata model mapping, either FGDC <-> ISO, or FGDC->DC, then DC->ISO. Doing the latter can ensure that any metadata model maps to/from DC, thus bypassing the requirement to do mappings for each/every/any combination of metadata model mappings.

It's a given that mappings will not be lossless, but a best effort. It would be valuable to establish these mappings across CSW servers for greater interoperability. I'd be willing to contribute here.