update of release notes for 3.16.0 (automatic)

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
update release notes for 3.16.0 (human)

Manual edit of the release notes to hopefully make
them more useful.  Also added reminder about the
deprecation of the prog and CCSR public catalog
themes.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>