Clean up demo app and migrate to gh-pages

* Restore Addepar app styles (fixes font and coloring problems)
* Fix usebanner in Gruntfile (no more disappearing headers)
* External links now link to other repos' gh-pages
* Use grunt-release-it instead of release-it
* Update README to point to new docs and describe new release process
* Allow for large hero on overview page
* Separate navigation/footer into their own partial views
* Move some dependencies and clean up build process a bit