Add graphite, scalable realtime graphing service
Add /etc/ssl/certs/ca-certificates.crt symlink for Ubuntu compatibility

NixOS and Fedora uses .../ca-bundle.crt. Ubuntu uses
.../ca-certificates.crt. Add .../ca-certificates.crt symlink to be
compatible with Ubuntu.

Example use case: Bob has a ~/.msmtprc file that he brings over from
Ubuntu. It also works on NixOS.
Revert "Add /etc/ssl/certs/ca-certificates.crt symlink for Ubuntu compatibility"

This reverts commit 10133f0b5b30e4d36a0c66742e1483d126d86f28.

See discussion at https://github.com/NixOS/nixos/pull/224
graphite: Refactor options, serve with waitress
merge
Fix typoe in graphite module (cabon -> carbon).
networkmanager: Add option for appending DNS settings

If the option is enabled, the DNS servers from networking.nameservers
will be inserted in /etc/resolv.conf after the DNS servers that
NetworkManager receieves by DHCP, or that is configured manually
in the connection settings.
Manual: Describe NixOS package management styles
Manual: Document user management
Manual: Document X11 configuration
Manual: Document LUKS encryption
Manual: Remove "bleeding edge" remark
Manual: Add section on how to do rollbacks
nixos-help: Use xdg-open if available
Manual: Move NVIDIA stuff into its own subsection
Manual: Document synaptics support
Manual: "filesystem" -> "file system"
Manual: Kernel configuration
Manual: Nix store maintenance
Manual: Document how to repair a corrupted Nix store