webadmin: Correct timezone default in New/Edit VM dialog

Correct setting of default timezone for windows type OSs with vdc_option
DefaultWindowsTimeZone. (renamed from DefaultTimeZone)

Also added new vdc_option DefaultGeneralTimeZone for default value of timezone
for general OSs (non-windows) using standard java timezone format.

Changed renderer to render the null field representing default engine timezone
with descriptive string to user.

Refactored majority of timezone-handling code from VmModelBehaviorBase to newly
created TimeZoneModel that caches all timezones and defaults, resulting in
improved performance of the dialog.

cleanup:

All references to TimeZoneInfo were replaced by usage of
DefaultWindowsTimeZone (or DefaultGeneralTimeZone, depending on OS type) and
the class itself was removed.

Removed the class TimeZoneMapping and its usage in REST api mappers since
the mapping was incomplete (there is no one-to-one mapping between Windows and
Linux/Java timezones, you can only have correct windows->java translation) and
even the usage of it was incorrect because it was converting the timezones to
windows format regardless of the OS-type.

Change-Id: Iaccb31f5634c16583004a79b9b47b83ff994088a
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=873795
Signed-off-by: Martin Betak <mbetak@redhat.com>