browserify build + commonJS require + restructuring

Another messy commit. Mostly moving around/renaming files to reflect the `AudioKit` structure.

The interesting part is the browserify build. I have found a hack to integrate scripts loaded with the `<script>` tag (our browser dependencies) to the browserify bundle.

For example, to have underscore available, you just need to include a file that exports it, like so : 

```javascript
// exposing underscore.js to the browserify bundle
module.exports = window._
```

Those files are created automatically by the task `"browser-dependencies-export"`. It's not super beautiful, but not that complicated either, and most of all it works.