Fix bugs related to TZ handling for all-day events

* In bug 2703075, all-day events from time zones at GMT or later
  appear a day early; this is because the time was calculated from
  the GMT date/time of the event rather than the local date/time of
  the event; this CL correctly changes this to use local date/time
* In bug 2707966, device-edited all-day events disappear in Outlook
  and OWA after upsync; this is due to the fact that we store all-day
  events in UTC on device, whereas we need to upload all-day events
  using the original (local) time zone.  In this CL, we save away
  the original time zone and use it on upsync
* In our decoding of Exchange time zone information, we default to
  local time when we can't find a time zone that matches the bias
  and DST information; we should really default to a time zone with
  the same bias, if one exists; we do that in this CL.
* Add/modify unit tests

Bug: 2703075
Change-Id: Id80c481ecc0eae980b2e91dae7f105f924cfca28
3 files changed