[snap] pull the desktop-qt5 part in

snapcraft doesn't support remote parts any more, and there's no
extension (the replacement for remote parts) for Qt yet.

Signed-off-by: Michał Sawicz <michal.sawicz@canonical.com>

snap/snapcraft.yaml

@@ -75,6 +75,30 @@ parts:
     options:
     - INCLUDEPATH+=QtHeaders
 
+  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
+      - locales-all
+      - xdg-user-dirs
+      - fcitx-frontend-qt5
+
   libdc:
     plugin: autotools
     source: .