Generalize the setup up external links with translations

[WebDevJL]

Generalize the setup up links, external only, with translations.

For a given link, the client enters in the administration site, via the ""Translations> Grid"" menu:

• a value ""visible text of the link"" (eg footer_partner_a_link1)
• a ""link URL"" value (eg footer_partner_a_link1_href)"