uigetdatetime launches a calendar widget to select a date/time

Calling Syntax
`newTime = uigetdatetime()` launches a calendar widget with the current date and time as the initially selected date/time at 0 hrs offset from UTC

`newTime = uigetdatetime('displayTime',t)` launches a calendar widget with t as the initially selected date/time at 0 hrs offset from UTC where t is a matlab serial date (datenum), datestring (datestr), or datetime object

`newTime = uigetdatetime('displayTime',t,'displayTimeZone',tz)` launches a calendar width with t as the initially selected date/time with UTC offset associated with string tz where tz is a java timezone string. to see a list of allowed timezones: tzList = cell(java.util.TimeZone.getAvailableIDs)

copyleft 2018 Peter Cook (peter DOT cook AT colorado DOT edu) with help from Yair Altman (altmany AT gmail DOT com)