Upstream merge (Cron configuration)

Full, cleaned-up pull request with the following new features and fixes:

* Addition of (optional) "cron" section in config file, which allows "time" in 12:34 format OR full "crontab" format such as `34 12 * * *` to support e.g. weekly backups. Defaults to midnight if no "cron" section specified, as per previous behavior.

* Made specification of "timezone" in "cron" config optional, removed package dependency on npm 'time' module (it's a C extension), documented that use of optional "timezone" requires `npm install time`. Default is to use host machine's local time rather than previous behavior of hard-coded US Eastern timezone.

* Application script itself now exits on completion when used with the -n (now) flag to support launching from actual unix cron (rather than running as a long running "daemon" with our own homegrown cron), including proper exit status code on error.