Clean up script/css imports

While poking around for the Foundation version (it's 3), I realized the
foundation.js we pull into the project has a version of jQuery and
Modernizr bundled into it.  It appeared that those were the versions
that we ultimately referenced on the page, so I removed the duplicate
declarations.  Presumably, this is not an ideal situation but I think it
should be resolved in a larger script issue (minifiying/concat).
Add dropdown menu plugin

The version of foundation we are using does have a dropdown component
so I added a small jQuery plugin for the functionality required for the
menu
dropdown feature.
Update region schema for menu header links

There is some new duplication with specifying the content of
header link menu items, which are also header links.  This
json is consumed server side and I did not want to attempt
JS execution to dynamically produce the result, as we've done
for some plugin schemas.
Add dropdown menu option for header links

To support the CoastalResilience feature of a configurable "Go To..."
link which will allow users to navigate between different C.R. regions,
I added this general purpose drop down link.  It does not support
nested dropdowns, as it was more compliated and the original feature
wasn't requesting it.