Dates expanding to expose some time (HH:MM:SS) granularity.

Dates expanding to expose some time (HH:MM:SS) granularity.

t/Dates.t is essentially restored from its previous state with
the revision that it now does not use C4::Context or check syspref
for the default date format.  Instead it sets the C4::Dates default
directly, taking cue from command line argument or ENV.  ISO format
revised to accept "T" separator and "Z" (zulu) terminator. POD
expanded and corrected.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>