Create new page in admin UI for link management

[jonstout]

This requires a bit of UI work, but the patterns are pretty standard at this point:

• Create link in admin ui navigation for Links page
• Create <LinkProvider render={links => console.log(links)} /> component to fetch link data
• Create <LinkTable links={[...]} /> component to display links
• Add Edit Link button to LinkTable rows
• Add Decommission Link button to LinkTable rows

This will additionally require some cgi work:

• Create webservice/link.cgi
• Create get_links function
• Create get_link function
• Create edit_link function