Additional display options for select options in form field

[cornelisonc]

Add display options for form field to conditionally show/hide offsets or names of timezones -- being able to remove the offset is particuarly helpful for users re: visual clutter.

[cornelisonc]

@andreia Done -- although I wasn't able to mirror the styles of your screenshot exactly, you may want to implement and take your own. How does that look?

[andreia]

@cornelisonc Looks great, thank you! I'm merging now, and I'll update the screenshot to match the style later