7066: use sdn module from Calendar package on pypi

Unfortunately, no package on ubuntu for sdn...

Bug fixed on trunk, when sdn is present on the system.
Verified that sdn roundtrip works.
date_test now fails on 1789-13-4(French) recognized as invalid,
as it probably should -- I guess this one is a test bug.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23127 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
7066: fallback to buggy PyICU if sdn unavailable

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23128 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
7066: some massaging of ICU version, still fails

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@23129 4ae1f11a-8b86-4847-b8af-ab372f36d1fd