Link member contacts from "about" menu

[JeremyMcCormick]

Add member organizations under about/member-organizations.

[molinaro-m]

While giving a go to this, I realized I cannot find the member-contacts page.
Unless I lost it in some other issue (if so, let me know) I plan to do both pages in the branch to cover this issue.

[molinaro-m]

From @JeremyMcCormick (commenting the closed #87 PT):

• about/member-contacts is not linked from the navigation menus, only from about/what_is_ivoa
• you may want to add a link to the navigation menu for that page so it is more easily accessible

I'm not sure it is useful, maybe we can discuss pros/cons before this change.
I re-open this issue, changing title, to keep this part open.