sass without bootstrap support, fixed requirejs errors without bootstrap...

Friends,

Now I know most of you opt for Twitter Bootstrap because it's so popular for fast prototyping, but a small minority of us rebel outsiders don't actually use it (or maybe it's just me, alone, unwanted), which makes me grateful for the choice  when running `yo`. So I decided to jump in here and make some tweaks to hopefully improve the experience a little for those of us who don't want Bootstrap when scaffolding out `yo webapp`.

This pull request makes a few minor suggested changes to `/app/index.js`:

1. It removes `<li>Twitter Bootstrap<li>` from the `<ul>` on index.html if Compass for Bootstrap was not installed on the CLI
2. It enhances the CSS of index.html if Bootstrap was not installed to have nicer formatting (at present, shamefully imitating the Bootstrap-equipped version)
3. It fixes a bug in which main.js still had bootstrap.js as part of the requires, causing 2 JS errors, the first a 404 to the nonexistent "bootstrap.js", the second an error from RequireJS about the same
4. If Compass for Bootstrap was not installed, since Compass is still part of "package.json" we can still assume that the project will use SASS/Compass, so both a .scss and a .sass version of the default styles are placed in /app/styles folder (yes, I prefer the older indented syntax, because I'm odd)

I've tested this and found no errors, and I hope it proves useful!