bug 3141: use quoted printable encoding in cart/list emails

bug 3141: use quoted printable encoding in cart/list emails

Ensure that emails sent from lists and the cart in the
OPAC have the correct quoted-printable encoding.  Otherwise,
if there is an equals sign followed by one or two characters
that look like hexadecimal digits in body of the email, the
results can look mangled in some email clients.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>