[Design] [Sum] Default TZ and interop

[Sheila Mooney]

I thought it was worth summarizing this thread.

+ Philippe had an event mailed to him that was at 3:00pm PST but in  
UTC (22:00Z). By default in Chandler, time-zones are turned off and  
we display events in floating time which means displaying the events  
without regard to time-zone. In this case, the event appeared at  
10:00pm instead of 3:00pm and was out of the field of view on his  
calendar so he couldn't see it. As soon as he turned on timezones,  
the event appeared at 3:00pm PST.
+ Philippe proposed that we turn on the display of time-zones by  
default so that the UTC time-zones would display correctly.

+ Jeffrey pointed out that Mimi would like us to handle UTC timezones  
differently so that when you receive one of these events AND have  
timezones turned off, it displays correctly in local time. This would  
have solved Philippe's issue regardless of whether or not timezones  
are turned on.
+ He also commented that in the "no time-zone" mode, we do preserve  
timezones, we just don't display them.
+ In certain cases, users don't always set their OS time-zone but we  
can't do much about that and it's likely rare.
+ He suggests a warning that appears when you receive an event in  
some other time-zone than your system time-zone prompting a user to  
turn on time-zones so the event displays correctly.

+ Mimi thought that was a good way to differentiate differentiate  
between:
	+ people who haven't turned on timezones because they don't know it  
exists
	+ people who specifically don't want timezone support.
+ Mimi also provided a layout for a dialog.

So, the proposal is....

+ Prompt the user if they DON'T have time-zones turned on and receive  
and event in some other time-zone. Anybody that cares about timezones  
and turns them on automatically won't see this dialog. There is still  
some question about whether or not we display this dialog when an  
event in created or when such an event is first displayed (I will  
clarify this with Mimi when she gets back).
+ Handle UTC timezones differently. This means that events in UTC  
will display correctly if the user happens to get the dialog above  
and doesn't want to turn on timezones.
+ If some people don't set their system time-zone, we won't worry  
about that use case since it's probably rare.

We haven't yet decided whether to go ahead and make these changes and  
for what milestone. I will work with the devs to figure out the scope  
and possible scheduling.

Sheila