Add support for upcoming icat.server 6.2

[RKrahl]

Add support for ICAT schema changes expected in upcoming icat.server 6.2.0:

• include Subject into dump file created by icatdump,
• add XML Schema Definition for the ICAT data file format in version 6.2,
• add examples for the new entity classes and attributes to the example data being used in the test and provide accordingly updated versions of icatdump-6.2.* files.

Draft, still to do:

• wait for the actual release of icat.server 6.2.0, update icatdump-6.2.* files, update the references to the ICAT version from 6.2a0 to 6.2 in conftest.py and test_06_query.py,
• review and update documentation.

Close#168.