Rename media mixin to media-down

This mixin handles adding media queries in a desktop down pattern. It
was getting confused with and overwrote the `media` mixin from the
toolkit. This should mean that one won't be able to clobber the other
based on include order.
IE6 fix

The width of two 50% elements wasn't working in IE6. Changing it to 49%
has no visually difference and makes it work.

Also changing the class to stop inheritance hurting it.
Hide label when there is content in search input
Add non-JavaScript fallback to input focus

Without this the text would apear ontop of other text when the input had
contents but wasn't focused.

Also wiggled the logo around.
Move navigation logic into slimmer

Slimmer will now move the navigation into the template. There is a
template for slimmer to take the downstream applications menu and wrap
it ready to be inserted.
Use mixins from toolkit for vendor prefixs
Retina-ready search icon
Use turquoise for header bar
Bump toolkit and allow desktop styles in ie6

Bumping the toolkit gives us the ability to send desktop styles to ie6.
It also gives us the `calc` css selector.