Add service.logind.extraConfig option

So that we can customize systemd-logind in configuration.nix.

Example:
  services.logind.extraConfig = "HandleLidSwitch=ignore";

See man logind.conf for available options.
bring bridge interfaces up

The bridge is not becoming operational until it is brought into the UP state.
When the bridge is statically configured, this is mandatory.
modules/testing/minimal-kernel: linuxPackagesFor no longer takes a 'self' argument
systemd-logind: fix config file header: [Logind] => [Login]

man logind.conf clearly states that the header is [Login] (no 'd').
Without this fix services.logind.extraConfig does not take effect
because logind ignores the invalidly named section.
Add a module for setting sysctl parameters

This adds an option ‘boot.kernel.sysctl’ and generates a file
/etc/sysctl/nixos.conf read by systemd-sysctl.service.
Enable hardlink and symlink restrictions

This prevents many time-of-check-time-of-use security bugs.  Ubuntu
enables these by default as well so they shouldn't cause many
problems.
installation-cd-base.nix: Use boot.kernel.sysctl
add most basic nginx service
Merge pull request #114 from iElectric/nginx-service

Add most basic nginx service