core: Move user and system snippets to subdirs

Instead of using ~/.emacs.d/$USER and ~/.emacs.d/$HOST, move the former
to ~/.emacs.d/users/$USER, and ~/.emacs.d/hosts/$HOST instead.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
algernon: Move bomadil settings to users/algernon/hosts/

The bombadil settings are not only host, but user specific too. Move
them to users/algernon/hosts/, and add a few lines to load host-specific
settings for the algernon user.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>