Consider updating assets directory names

[LukeAskew]

Folder names like scss and js couple the language to the code a little too closely and can cause a some confusion if the end-user wants to use less or coffeescript.

Instead, consider using styles and scripts.

[nicetransition]

I've debated this constantly, with the current useage of JS/CSS and compilation tools/frameworks it makes since to move to the styles and scripts because "/js/" might include more than just a *.js and the same for "/scss"

[nicetransition]

Once you're ready, it might be good to make this a variable in Yeoman