(WIP) Loader - incorporate pathogen encoding logic in a separate module under loader.

This is a follow up to https://github.com/yui/yui3/pull/1813. 
I created this pull request specifically for feedback as to the direction that needs to be taken.

@caridy
@juandopazo
@ekashida
ops, I change my mind :) due to the `loaderPath` definition that is required because there is not a loader to compute the url of it dynamically, that's a boomer.

I think the only solution is to let them define the path of the seed per app (as I described above).