* helm-source.el: Add classes for type with access functions.
* helm-source.el: Introduce new slots before/after-init-hook.
* helm.el (helm-initial-setup): Run local source hooks.
* helm-files.el (helm-source-find-files): now nil.
(helm-find-files-1): Setup source here, add it the init hooks.
Use helm-build-type-file to build type file.