[FIX] website_mail: sanitize email templates when displaying templates selection

In cases the templates is not html syntax valid
[FIX] website_mail: t-field replace by t-esc as html_sanitize applied on the field
Fix two possible AsciiErrors when an exception occurs

Signed-off-by: Sandy Carter <sandy.carter@savoirfairelinux.com>
Merge pull request #2620 from savoirfairelinux/8.0-http-unicode

Fix two possible UnicodeDecodeError when an exception occurs
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64