[FIX] mail: linkify livechat message so frontend has them

In ff56304f a solution was tried to have message posted from
backend livechat linkified for visitor in frontend. This was
forward-ported when it should not have been and introduced issues
including:

- `href="{link}"` would become `href="<a href="{link}">{link}</a>"`

- if html entities such as the ones for U+00A0, and entities <, >,
  ', " or ` were next to the link, the entity would be linkified
  too (up to the ;)

This happen because utils.linkify function is to be used with text
content and not html which was the case in this instance.

opw-693457
opw-702410