Refined project footer navigation, responsive styles

@ldamon could you review on Monday? thx

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* Removed redundant arrows on the first and last project pages
* Added hover states to next and previous project titles plus "back to work"
https://github.com/jekyll/jekyll/issues/32

^ This feels similar to the issue you're dealing with. Can you use "includes" to add the nav arrows as a partial, instead of a whole new layout?