Add option to obfuscate email addresses domain

The email obfuscator are currently hiding only the local part of the email address.
There must be an option to obfuscation the domain of the email or the full email string.

It's currently done by using a regex in DefaultEmailAddressObfuscator :

return emailAddress.toString().replaceAll("^(.).*@", "$1...@"); 

Proposals :
1. Add domain obfuscation option in administration (Global Administration → Mail → Advanced)
2. Add key in xwiki.properties to define a custom regex for email obfuscation.