Flatpak: Add appindicator plugin

Modules are copied from https://github.com/flathub/shared-modules

flatpak/org.gajim.Gajim.Plugin.appindicator.yaml

@@ -0,0 +1,34 @@
+id: org.gajim.Gajim.Devel.Plugin.appindicator
+runtime: org.gajim.Gajim.Devel
+sdk: org.gnome.Sdk//3.36
+build-extension: true
+separate-locales: false
+appstream-compose: false
+
+build-options:
+  env:
+    PYTHONPATH: /app/plugins/appindicator/lib/python3.7/site-packages/
+  prefix: /app/plugins/appindicator
+  prepend-pkg-config-path: /app/plugins/appindicator/lib/pkgconfig
+  prepend-path: /app/plugins/appindicator/bin
+
+modules:
+  - modules/libappindicator/libappindicator-gtk3-introspection-12.10.json
+
+  - name: gajim-appindicator
+    buildsystem: simple
+    build-commands:
+      - 'cp -R -t ${FLATPAK_DEST} *'
+    post-install:
+      - install -Dm644 --target-directory=${FLATPAK_DEST}/share/metainfo org.gajim.Gajim.Plugin.appindicator.metainfo.xml
+      - appstream-compose --basename=org.gajim.Gajim.Devel.Plugin.appindicator --prefix=${FLATPAK_DEST} --origin=flatpak org.gajim.Gajim.Plugin.appindicator
+    sources:
+      - type: archive
+        url: https://ftp.gajim.org/plugins_releases/appindicator_integration_1.3.2.zip
+        sha256: d56e1af24cc462d2090b33c53c6dd9f2a00d38c6c35aaa616d021c5f069a2333
+      - type: file
+        path: ../appindicator_integration/org.gajim.Gajim.Plugin.appindicator.metainfo.xml
+        sha256: 8591662b70ac496a2411ced0e08fa630744416eb3f301c006e12207ee84cecbf
+      - type: shell
+        commands:
+          - sed -i "s+org.gajim.Gajim+org.gajim.Gajim.Devel+" org.gajim.Gajim.Plugin.*.metainfo.xml