bash: Source nix profile.
fluxbox: Move into host-based conf.
bash: Include a host-specific configuration.
parcellite: Move into host conf.

It's fragile across upgrades. Install with:

    mkdir -p ~/.config/parcellite
    cd ~/.config/parcellite
    rm -f parcelliterc
    ln -sf ../host/$HOSTNAME/parcelliterc .
emacs: Remove menu-bar in emacs24.