Fixing the email address property validation.

Fixing issue: http://issues.umbraco.org/issue/U4-5364

Also added appropriate code for Localization and added localization strings to the en & en_us language files.
I've added the task here as a high priority and targeted at 7.2.1 - hopefully this will stay as high priority after we chat with @nul800sebastiaan 

http://issues.umbraco.org/issue/U4-5966