Added timezone prompt to quickstart

This implements one of the improvements suggested in Issue no: #1337.
Asks user for timezone during the quickstart process.
It also validates input time zones by checking if they exist in the pytz.all_timezones list
(white-space and case insensitive)


If the user enters an invalid timezone, it prompts the given url which contains a list of valid timezones (as mentioned in the documentatioon)