[fix] Mail helper is not synced with email validation

The local part of an email (text before the "@") may include any of the following characters
( http://www.w3.org/TR/html-markup/input.email.html )
Uppercase and lowercase English letters (a–z, A–Z)
Digits 0 to 9 
These special characters: ! # $ % & ’ * + - / = ? ^ _ ` { | } ~
Character . (dot, period, full stop) (ASCII: 46) provided that it is not the first or last character, and provided also that it does not appear consecutively (e.g. John..Doe@example.com is not allowed).

After correcting the validation (See https://github.com/joomla/joomla-cms/pull/4894 and https://github.com/joomla/joomla-cms/commit/6ba7987c142e5e859da52a33c5b7f7c62f1d1e64 ), we still could not save an email containing for example any of these in the local part.
`/{|}~-^`
This patch will allow using them. It will also take care of the double dot and dot as first character.
JM Isn't the comment here with the symbols removed in #4894 ?