When importing ICS files, map "W. Europe Standard Time" to "Europe/Berlin"

Summary: Ref T11816. See that task for discussion. If we get a few more of these I'll try to mangle in a big list of Windows timezone names.

Test Plan: Looked at timezone offsets in VTIMEZONE, matched them up to CET/CEST offsets.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11816

Differential Revision: https://secure.phabricator.com/D16865