Add support for timezones

[ngsilverman]

I noticed that the displayed time of some of my events were off. This has gone through minimal testing but it fixed the events I was looking at, so hopefully it goes in the right direction even if it may not yet work in all cases.

This approach uses the timezone information from ICS to properly convert ical.Time objects to UTC, from there it uses the local timezone to convert those into accurate dates and times for human consumption.

TODO

• Update tests: I tried updating the snapshots but since the current change uses the local timezone something needs to be figured out to make the tests consistent. Probably the tests should be based on UTC and the local timezone conversion can happen separately.

Possibly Related

• ICS events appear in the wrong timezone #311
• Use the users local timezone for non recurring ics events #464
• Google events don't show up in the correct day, without a pattern i can notice. #483