Time zone conversion

As a CSM I need to log activities and emails according to my client's time zone so I can reference the time in a meaningful way to my clients.

Acceptance criteria:
Convert times entered in my local time zone to the client's time zone
Display both times in Activities and CoPilot
Allow a toggle between my time zone and client local times in Global timeline

Examples:
My client on the west coast and I am on the east coast.
1.  I refer the client o an email was sent in the time according to my time zone.  The client is unable to find an email at that time because of the difference in time zone.
2.  I refer to a meeting from Activities in eastern time and the client thinks they did not attend because they do not see any meeting at that time on their calendar.