Fixes #91 #102 - Compile JS and CSS sources on request if modified

Very rough fix. Will clean up later.

Passes requests to the same functions that the helperContexts use (ie. `css()` and `js()`) to compile the assets. If there is a change, Snockets will detect it and recompile. 

Request is then served by `connect-file-cache` as usual.

TODO: Fix the path logic