fix navbar active selectors (bug 1090027)
fix Dockerfile
Fix navbar rendering when navigation.stack is empty (bug 1088419)

It shouldn't happen, but we have evidence that it does, my guess
is that there is a race condition somewhere causing the navbar to
be rendered before navigation stack is built.
remove old waffle test (bug 1091139)
improve CSS for site navigation bar (bug 1082161, bug 1083613, bug 1083614)

* remove unused rules, optimise selectors, and make things more OOCSS-y
* improve navigation hover states (bug 1082161)
* use CSS instead of JS to toggle category drop-down on desktop (bug 1083613)
* add borders to desktop navigation items (bug 1083614)
* fixed CSS to actually hide the link outlines on focus
* remove `cur-cat` class and use more descriptive classes
* remove specificity all over the space to reduce complex cascading
* considerable clean up to `sprite-background-position` for category icons