Improve contacts page structure and roles

[molinaro-m]

In porting to markdown the (former) HTML pages the "about/contacts" one needs some attention.

A list of things to consider are:

• the document coordinator is also the contact point for web content, i.e. web admin
• "technical leads" can be misleading, i.e. confused with web admins
• the "2 columns" structure currently on the page mixes up boards and duties

[molinaro-m]

the contact page is translated (basic, PR #86), and its content reflects current roles
it can be improved, but that is content-wise, not md translation