[#46,content][l]: major refactor of site content to focus (back) on data more.

* Home page just has a hero section with main message which is the data one (key datasets in high-quality ...)
* Merge a bunch of the home page stuff into about
* Get involved info off front page and merged into contribute page (which was heavily refactored)
[theme][m]: switch to use okfnlabs.org look and feel.