Add Nightwatch functional browser tests to test Fauxton

This commit adds a basis for using Nightwatch's functional
browser testing environment to test Fauxton.

Closes COUCHDB-2369
add license headers
Updated style guide to include HTML and CSS sections

Closes COUCHDB-2416
Feedback from @robertkowalski
bulkdelete: add basic integration test

This adds a basic integration test for bulk-deletion of docs

COUCHDB-2462
Fix ACE document editor cutting off long lines of code

Closes COUCHDB-2454
Enable passing a single test to nightwatch

You can now pass single testfiles to nightwatch which makes
development of tests easier and faster.

Example:
`grunt nightwatch --file="createsDatabase"` launches the
createsDatabase.js testfile in app/databases/tests/nightwatch

Happy testing!
new design for docs
wip
easier customization
styling: labels / checkboxes
fix change event
show-select & select-all
whitespace
change behaviour of select-all