Merge of ISO 19115-3 work to JDK8 branch

[Martin Desruisseaux <ma...@geomatys.com>]

Hello all

ISO 19115-3, published in 2016, is the new XML format for geospatial
metadata. It replaces the legacy ISO 19139 format published in 2007.
Apache SIS currently supports only that legacy format. The work on ISO
19115-3 [1,2] (based on ImageMatters contribution) is close to
completion. We still have test failures to fix on the ISO 19115-3
branch, but I think it will be finished today. Once the tests are fixed,
we will be ready to merge to the main SIS branches (JDK8, trunk). This
will be a major merge, with about 520 classes impacted. The consequences
for peoples using XML will be:

  * Nothing changed for reading legacy ISO 19139:2007 documents; Apache
    SIS should read transparently both the old and the new formats.
  * Nothing to do for reading new ISO 19115-3:2016 documents; it will be
    recognized automatically.
  * When writing XML documents, the default format will now be the new
    format instead than the old one. For formatting metadata in the old
    format, it will be necessary to ask explicitly.

If everything goes well, the merge could be done Friday or Saturday. Is
there any objection to that approach, or things that people wish to change?

    Martin

[1] https://svn.apache.org/repos/asf/sis/branches/ISO-19115-3/
[2] https://github.com/apache/sis/tree/ISO-19115-3