This patch allows email adresses of the form john.public@company.hamburg
This fixes the bug: https://bugzilla.proxmox.com/show_bug.cgi?id=716

Note that this patch only deals will the client side validation, a
separate deals with the server side validation
(http://pve.proxmox.com/pipermail/pve-devel/2015-September/017246.html)

Implementation:
Just copied the original email regexp from ExtJS, and bumped the TLD length
from 6 to the max allowed by the corresponding RFC, ie 63 (https://tools.ietf.org/html/rfc1034)