Don't rely on classList in fabricator.js

[tylersticka]

classList is awesome, but it isn't fully supported in any version of IE.

For most projects I would opt for a polyfill, but I think that could be confusing given that most of our Fabricator styles and scripts strive to not litter anything global to avoid confusing what is or isn't part of the project toolkit. Something like the classlist module might be a more appropriate choice, though I'll defer to @erikjung if he feels strongly either way.

See also: #14 #18