refactor docs (no content or style changes)

inherit from a common base, move footer to an inclue, add comments to CSS for readability, and introduce a guide-base from which guide-normal inherits
combining style sheets and layouts, esp for user guide

user guide now has the same top+bottom branding as rest of site
add icon links for twitter, github, and IRC; and use scss, because jekyll allows

just using a bit of scss, but it looks like it can help a lot to ensure consistent colors

also restored helvetica neue is font of choice
link to repo GUI *and* to dir, simplify (a bit) how url's are computed, and tidy guide downloads page
notes on use of rdiscount and pygments (neither helpful though)
remove duplicate jquery js load

this was breaking superfish; but things seemed to be working, so maybe we don't need superfish!
fix navgroup id's so menu highlights correctly
Merge and close #408