Add DevHub to the w.org navigation menu

[johnbillion]

I mentioned this to Drew a while ago but forgot to open a ticket. While DevHub is still technically under construction, it's mature enough that we should add a link to it to the main navigation menu across w.org.

The Codex currently occupies the 'Documentation' submenu under 'Support', so I think a new submenu called 'Developer Resources' should be added which points to developer.wordpress.org.

[DrewAPicture]

FWIW, there's already a link in the global footer.

[samuelsidler]

We aren't adding more things to the Support drop down and, in fact, want to remove it entirely. There are some design changes we can make on /support/ in the not-too-distant future to showcase devhub.