[feature]Store and present datetime with timezones

[leeenglestone]

At the moment, all times are relative to the events "location".

We need to start storing the timezone along with the datetime.

[leeenglestone]

https://publib.boulder.ibm.com/tividd/td/TWS/SC32-1274-02/en_US/HTML/SRF_mst273.htm

I wonder if a drop down list of these would suffice, next to the date & time controls?