studio: nav - clicking anywhere but nav's dropdowns will close them, fixed link outline and is-selected styling

studio - soft landing and nav: slight visual tweaks to soft landing UI and added in support link + new tab/window and modal management JS

studio - course nav: corrected JS behavior of dropdowns to hide all others and self-hide appropriately

racing condition.

caveats: - it drops wherever the y of the cursor is no matter the x for
the cursor. I've constrained the draggables to never change x; so, the
drop doesn't care where the x of the cursor is only the y.
- if you force auto scroll, the visual thing you'll dragging gets out of
sync w/ the mouse cursor; however, the mouse cursor is the "true"
location; so, the drop's posit is the mouse cursor y not the visual
clone's y.

Unit drag and drop works correctly now.

https://edx.lighthouseapp.com/projects/102637-studio/tickets/135-via-tender-studio-asset-locker-currently-returns-incorrect-xml-snippet