kdeApplications.koi: init at 0.3.1

[Koi](https://github.com/baduhai/Koi) is a scheduling theme switcher for
KDE that I have been using on Plasma 6 for the last few days. It has
been working great for me, and I was originally looking for it within
`nixpkgs`, but couldn't find it, so here it is.

This is the derivation I have been testing it with:
7edb3f60a8

I have also been running it from my own development fork of `nixpkgs`
using the same code I'm submitting here.

pkgs/kde/default.nix

@@ -88,6 +88,7 @@ let
 
         applet-window-buttons6 = self.callPackage ./third-party/applet-window-buttons6 { };
         karousel = self.callPackage ./third-party/karousel { };
+        koi = self.callPackage ./third-party/koi { };
         krohnkite = self.callPackage ./third-party/krohnkite { };
         kzones = self.callPackage ./third-party/kzones { };
       }

pkgs/kde/third-party/koi/default.nix

@@ -0,0 +1,55 @@
+{
+  lib,
+  stdenv,
+  fetchFromGitHub,
+  cmake,
+  kconfig,
+  kcoreaddons,
+  kwidgetsaddons,
+  wrapQtAppsHook,
+}:
+stdenv.mkDerivation rec {
+  pname = "koi";
+  version = "0.3.1";
+
+  src = fetchFromGitHub {
+    owner = "baduhai";
+    repo = "Koi";
+    rev = version;
+    sha256 = "sha256-dhpuKIY/Xi62hzJlnVCIOF0k6uoQ3zH129fLq/r+Kmg";
+  };
+
+  # See https://github.com/baduhai/Koi/blob/master/development/Nix%20OS/dev.nix
+  sourceRoot = "source/src";
+  nativeBuildInputs = [
+    cmake
+    wrapQtAppsHook
+  ];
+  buildInputs = [
+    kconfig
+    kcoreaddons
+    kwidgetsaddons
+  ];
+
+  meta = with lib; {
+    description = "Scheduling LIGHT/DARK Theme Converter for the KDE Plasma Desktop";
+    longDescription = ''
+      Koi is a program designed to provide the KDE Plasma Desktop functionality to automatically switch between light and dark themes. Koi is under semi-active development, and while it is stable enough to use daily, expect bugs. Koi is designed to be used with Plasma, and while some features may function under different desktop environments, they are unlikely to work and untested.
+
+      Features:
+
+      - Toggle between light and dark presets based on time
+      - Change Plasma style
+      - Change Qt colour scheme
+      - Change Icon theme
+      - Change GTK theme
+      - Change wallpaper
+      - Hide application to system tray
+      - Toggle between LIGHT/DARK themes by clicking mouse wheel
+    '';
+    license = licenses.lgpl3;
+    platforms = platforms.linux;
+    homepage = "https://github.com/baduhai/Koi";
+    maintainers = [ ];
+  };
+}