Cleanup: remove unused index.html

I first noticed an unused footer element, but it turned out that
the whole `index.html` file was unused (it is now generated by
`index.underscore`)
Replace .execute() for .click() behavior in Nightwatch tests
Cleanup: Remove unused nv.d3

stats are removed now and we don't use it any more

Closes COUCHDB-2355
New design for docs

Port from #33:

Based on the work of Jenn Schiffer <jenn@pancaketheorem.com>
(@jennschiffer), Sue Lockwood <deathbear@apache.org>
(@deathbearbrown) and Sean Barclay (@seanbarclay)