update css/html
comment out demo section, tweak footer

- use array for footer nav links to control ordering
- ditch github developer wiki button, should be replaced with star and fork
  widgets
- ditch 'some rights reserved'
move hard-coded strings into translations.js
tweaks to download section

- collapse "installer data not (yet) loaded" and "error loading installer
  data" into a single "no installer data" state, and show "check back again
  soon" for it
- basic validation of installer data
- hook up os icon to selected os
refactor installer data fetching into a service
small refactor (constants, footer) + github ribbon