Bug 1853138 - Switch to Email::Address::XS (#160)

Bug 1853138 - Switch to Email::Address::XS (#160)

* Bug 1853138 - Switch to Email::Address::XS

This patch updates us from using Email::Address to Email::Address::XS to
resolve CVE-2015-7686.

Regex comparisons have been replaced by parse + is_valid calls as per
current documentation.

Email::Address->parse($string) used to parse all addresses out of a
general string, however Email::Address::XS expects the string to only
contain addresses in the verious forms.

This patch uses a basic regex to parse out strings that look like email
addresses from the overall string passed, before passing to
Email::Address::XS for validation and splitting out the 'host' part of
the address.

This patch restores the Email::Address::XS entry in Requirements.pm so
that we can specify which version of the module we wish to use and make
it explicit that we're using the module rather than relying on
Email::Sender pulling it in for us.