DONT MERGE: Dev asset non-compilation

Hacked about to get a proof-of-concept non-compilation of assets working, i.e. modules are pulled in when needed.

However, because we have so many modules, it's now actually slower as each module it pulled in. The upfront compilation, now we switched over to grunt, is now actually pretty quick. So after all this I'd say we should stick to compiling on dev. 

However, there are a couple of things we should do

 * don't minify js - `"optimize"  : "none"`
 * add source maps to js (http://requirejs.org/docs/optimization.html#sourcemaps) and sass
 * look into tightening up the asset hashing - each request seems to set it off multiple times; it only needs to be created once, when a file changes