making time_zone and first_day_of_week configurable

@zeb requested TIME_ZONE being configurable via ```bin/omero config set omero.web.time_zone``` to avoid local code changes.
Might want to use docs from a new version. 8.1 is so old that we don't even support it, though it seems odd that http://www.openmicroscopy.org/site/support/omero5/sysadmins/system-requirements.html doesn't mention that.