update `contacts` data and/or display

[PascalinDe]

contacts is a list, with

• a required name,
• an optional email,
• an optional url

but we only use the very first item in the list, and display the email field (broken if there is only a url field)

some thoughts on this:

• making the e-mail field required (currently semi-implemented)
• OR displaying either the e-mail field or the link if there is an URL instead of an e-mail
• adding a tab for contacts to the project page, and linking to that if more than one contact is in the list

@ineiti what do you think?