Allow for email sent to merchant to have labels in his own language.

Take note that only 'email' and 'body' are validated in the contact
form, so we must use a name attribute set to 'email' and 'body'
respectively for those. Every other field can use any other name
attribute. Shopify has no particular concept of a 'phone' field or
'name' field. So use localization there! Also I added placeholder
translations, since the form fields were re-using the label as
placeholder, which is I think was “lazy”-ish of us.