Fix vCard group support as defined in RFC 6350 § 3.3
Fix vCard group support as defined in RFC 6350 § 3.3

A lot of vCards, especially those created by Apple software, use the
visual grouping feature. The field types are essentially prefixed with
the name of the group followed by a period.

Add group detection and strip it off when encountered.

RavenB/Z-Push-contrib,mta59066/Z-Push-contrib,Freeaqingme/Z-Push-contrib,fmbiete/Z-Push-contrib