snap: Use kde-neon extension

The kde-neon extension reduces our boilerplate in snapcraft.yaml
and reduces the snap size considerably, as we do not need to ship
any library that is already included in the kde-frameworks-5-core18
snap itself.

This limits qelectrotech builds to the architectures supported
by kde-frameworks-5-core18, i.e. only amd64.

build-aux/snap/snapcraft.yaml

@@ -15,45 +15,31 @@ layout:
   /usr/local/share/qelectrotech:
     bind: $SNAP/usr/local/share/qelectrotech
   /usr/share/libdrm/amdgpu.ids:
-    bind-file: $SNAP/usr/share/libdrm/amdgpu.ids
-
-plugs:
-  gtk-3-themes:
-    interface: content
-    target: $SNAP/data-dir/themes
-    default-provider: gtk-common-themes
-  icon-themes:
-    interface: content
-    target: $SNAP/data-dir/icons
-    default-provider: gtk-common-themes
-  sound-themes:
-    interface: content
-    target: $SNAP/data-dir/sounds
-    default-provider: gtk-common-themes
+    bind-file: $SNAP/kf5/usr/share/libdrm/amdgpu.ids
 
 apps:
   qelectrotech:
-    adapter: full
     command: usr/local/bin/qelectrotech
     command-chain:
-      - bin/desktop-launch 
       - bin/qelectrotech-launch
     desktop: usr/local/share/applications/qelectrotech.desktop
-    plugs: &plugs [opengl, x11, unity7, wayland, desktop, desktop-legacy, home, removable-media, gsettings, network, cups-control]
+    extensions: [kde-neon]
+    plugs: &plugs [opengl, unity7, home, removable-media, gsettings, network, cups-control]
     environment: &env
-        __EGL_VENDOR_LIBRARY_DIRS: $SNAP/usr/share/glvnd/egl_vendor.d
+      __EGL_VENDOR_LIBRARY_DIRS: $SNAP/kf5/usr/share/glvnd/egl_vendor.d:$SNAP/usr/share/glvnd/egl_vendor.d
+      TCL_LIBRARY: $SNAP/usr/share/tcltk/tcl8.6
         QT_QPA_PLATFORMTHEME: gtk3
         QT_AUTO_SCREEN_SCALE_FACTOR: 1
-        DISABLE_WAYLAND: 1
-        TCL_LIBRARY: $SNAP/usr/share/tcltk/tcl8.6
 
   qet-tb-generator:
-    command: desktop-launch $SNAP/bin/qet_tb_generator
+    command: bin/qelectrotech-launch $SNAP/bin/qet_tb_generator
+    extensions: [kde-neon]
     plugs: *plugs
     environment: *env
 
   dxf-to-qet:
-    command: desktop-launch $SNAP/bin/DXFtoQET
+    command: bin/DXFtoQET
+    extensions: [kde-neon]
     plugs: *plugs
     environment: *env
 
@@ -64,34 +50,7 @@ parts:
     organize:
       '*': bin/
 
-  desktop-qt5:
-    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git
-    source-subdir: qt
-    plugin: make
-    make-parameters: ["FLAVOR=qt5"]
-    build-packages:
-      - build-essential
-      - qtbase5-dev
-      - dpkg-dev
-    stage-packages:
-      - libxkbcommon0
-      - ttf-ubuntu-font-family
-      - dmz-cursor-theme
-      - light-themes
-      - adwaita-icon-theme
-      - gnome-themes-standard
-      - shared-mime-info
-      - libqt5gui5
-      - libgdk-pixbuf2.0-0
-      - libqt5svg5 # for loading icon themes which are svg
-      - try: [appmenu-qt5] # not available on core18
-      - locales-all 
-      - xdg-user-dirs
-      - fcitx-frontend-qt5
-      - cups-bsd # for lpr used for printing in general (needs cups-control)
-  
   qet-tb-generator:
-    after: [desktop-qt5]
     plugin: python
     python-version: python3
     source: https://github.com/qelectrotech/qet_tb_generator.git