Add "no-js" class to Sequence element

Like Modernizr, add functionality to allow a Sequence element to be given the class `no-js` when JavaScript is disabled. Remove this class when Sequence is initiated.

This will make writing styles for non JS/JS a little more intuitive.

Start at the Sequence element initialization code and inspect how its classes are currently handled. Add the no-js class before initialization and remove it when Sequence starts; done means the class reflects whether JavaScript has initialized the element.

Written by the indexing model from the issue text.