Add "Eastern Time" to timezone mappings

[alecpl]

Here's sample of iCal data:

BEGIN:VCALENDAR
PRODID:-//Microsoft Corporation//Outlook 10.0 MIMEDIR//EN
VERSION:2.0
METHOD:REQUEST
BEGIN:VTIMEZONE
TZID:Eastern Time
BEGIN:STANDARD
DTSTART:20161101T020000
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=1SU;BYMONTH=11
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:Standard Time
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:20160301T020000
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=2SU;BYMONTH=3
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:Daylight Savings Time
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID="Eastern Time":20180430T100000
DTEND;TZID="Eastern Time":20180430T110000
...

According to one of our users it came from WebEX system.

I see that Eastern Time (US & Canada) already exists in exchangezones.php, but it does not match. Please, add an Eastern Time alias and also consider doing this for other timezones with similar problem.