SIMPLE and WHITESPACE builds

This PR enables running the examples hosted on http://openlayers.github.com against the `ol.js` build (ADVANCED compilation), as well as against `ol-simple.js` (SIMPLE compilation) and `ol-whitespace.js` (WHITESPACE compilation) builds. I think can be useful for debugging, and playing around with the examples.

Selecting the mode is done similarly as when using Plovr, for example: `full-screen.html?mode=whitespace`.

(Note that I still think we need more simplicity, see #241.)