[Suggestion] Add support for timezones in reminders

[williamjcm]

What I'd like to is be able to set reminders with a way to specify the timezone for reminders that should occur at a specific time.

For example, I'm living in the CEST timezone, and I set a reminder to occur at 09:00 several days from now. When I checked the reminder list, I noticed that the reminder's ETA corresponded to 09:00 either for the server or the bot, not my timezone.

Of course, adding CEST to the date/time parameter didn't work either, so I had to calculate the offset between my timezone and the one the bot had in mind just to make sure that reminder would occur at 09:00 in my timezone.

Sorry if some parts don't make much sense, but it's 01:02 in my timezone as of this writing.