Upgrade to Capacitor 7

Necessary workarounds:

- capacitor-navigation-bar: We now directly include a patched version of
  the plugin, as the original repo seems to be unmaintained atm and
  currently. The patched version works with Capacitor 7.
- We need to set the statusbar overlay to false on mount, as true seems
  to be the new default. Otherwise the top menu items would clip into
  the Android statusbar.

Closes #942

.github/workflows/pull-android.yml

@@ -37,7 +37,7 @@ jobs:
         uses: actions/setup-java@v3
         with:
           distribution: "zulu"
-          java-version: "17"
+          java-version: "21"
           cache: "gradle"
 
       - name: Build App