Creates a field and tooltip in
/admin/enterprises/<enterprise>/edit#!/contact for updating the
enterprise's WhatsApp phone number, with corresponding i18n keys for the
name of the field, placeholder and tooltip text.
Add a new column email_address to enterprises.
Use this new field for public display of contact details.
The old field enterprise.email is still used internally.
It is still displayed on orders and emails sent to customers.
A new enterprise has the owner's email address by default now.
Fix GH #757
