Time zone support

[jrubenoff]

Outcomes

• Avoid displaying every calendar invite in an arbitrary time zone that might be irrelevant to the customer (like GMT).
• Ensure applicants and interviewers are viewing time slots in their current time zone.

Structure

• Ask the admin to choose a time zone for their project.
• Ask everyone to choose their time zone before viewing time slots. (We can use the browser's locale to select a smart default.)

Interaction

We can take a page from Calendly's book, and make the time zone dropdown a nice selectize with optgroups for each continent / region.

[ajb]

I implemented this in the backend today, and actually found some flexibility where I didn't think we had it.

If we want, we can treat timezones the same way we do as in Screendoor -- instead of asking a user to set a timezone for their project, we can simply localize the times that they're choosing in the "Scheduling" setup page.

I previously thought that all calendar events needed to be in a specific timezone, but it's actually easier to just send the events in UTC -- and our users won't know the difference. I looked at a bunch of other calendar feeds, and none of them specify timezones either.

[ajb]

This issue was moved to dobtco/scheduler#5