(cherry picked from commit 88e7d7b)

(cherry picked from commit 011a463)

(cherry picked from commit fed0a4e)

(cherry picked from commit 97d2779)

(cherry picked from commit 3ad8afb)

(cherry picked from commit b4d4aff)

(cherry picked from commit 43d8a40)

(cherry picked from commit 0ba1f0a)

(cherry picked from commit 9dd5dc5)

(cherry picked from commit b3dff39)

Cross fixes for 18.09

(cherry picked from commit 2a4bfe20d5aa2709c40f4b1d2bf55b34d3131144)

(cherry picked from commit a25e765)

* skypeforlinux: 8.28.0.41 -> 8.32.0.44

Fixes 404 on https://repo.skype.com/deb/pool/main/s/skypeforlinux/skypeforlinux_8.28.0.41_amd64.deb, as only [more recent versions](https://repo.skype.com/deb/pool/main/s/skypeforlinux/) are still available, as previously noted at NixOS#31047. Avoiding `x.y.76.z` releases as per the comment.

* update sha256

(cherry picked from commit 72128fc)

This adds configuration options which automate the configuration of NVIDIA Optimus using PRIME. This allows using the NVIDIA proprietary driver on Optimus laptops, in order to render using the NVIDIA GPU while outputting to displays connected only to the integrated Intel GPU. It also adds an option for enabling kernel modesetting for the NVIDIA driver (via a kernel command line flag); this is particularly useful together with Optimus/PRIME because it fixes tearing on PRIME-connected screens.

The user still needs to enable the Optimus/PRIME feature and specify the bus IDs of the Intel and NVIDIA GPUs, but this is still much easier for users and more reliable. The implementation handles both the X configuration file as well as getting display managers to run certain necessary `xrandr` commands just after X has started.

Configuration of commands run after X startup is done using a new configuration option `services.xserver.displayManager.setupCommands`. Support for this option is implemented for LightDM, GDM and SDDM; all of these have been tested with this feature including logging into a Plasma session.

Note: support of `setupCommands` for GDM is implemented by making GDM run the session executable via a wrapper; the wrapper will run the `setupCommands` before execing. This seemed like the simplest and most reliable approach, and solves running these commands both for GDM's X server and user X servers (GDM starts separate X servers for itself and user sessions). An alternative approach would be with autostart files but that seems harder to set up and less reliable.

Note that some simple features for X configuration file generation (in `xserver.nix`) are added which are used in the implementation:
- `services.xserver.extraConfig`: Allows adding arbitrary new sections. This is used to add the Device section for the Intel GPU.
- `deviceSection` and `screenSection` within `services.xserver.drivers`. This allows the nvidia configuration module to add additional contents into the `Device` and `Screen` sections of the "nvidia" driver, and not into such sections for other drivers that may be enabled.

(cherry picked from commit 22c12da)

(cherry picked from commit 096be6d)
Reason: the package is broken in NixOS stable.

haskellPackages.shell-conduit: fix build

See https://docs.djangoproject.com/en/1.11/releases/1.11.16/

(cherry picked from commit 95a040f)

See https://docs.djangoproject.com/en/2.0/releases/2.0.9/

(cherry picked from commit cd90264)

See https://docs.djangoproject.com/en/2.1/releases/2.1.2/

(cherry picked from commit 50ad0f2)

(cherry picked from commit 2a2c996)

(cherry picked from commit 67f58ee)
Signed-off-by: Domen Kožar <domen@dev.si>

(cherry picked from commit 4ada74e)

(cherry picked from commit f14d3b4)

(cherry picked from commit 7a55215)

(cherry picked from commit fe847fc)

(cherry picked from commit 870f05c)

(cherry picked from commit 5f1013d)

(cherry picked from commit 2cd2571)