feat(U4): background sync and local notifications for new mail (#28)

android/app/build.gradle.kts

@@ -35,7 +35,7 @@ android {
         applicationId = "de.sharedinbox.mua"
         // You can update the following values to match your application needs.
         // For more information, see: https://flutter.dev/to/review-gradle-config.
-        minSdk = flutter.minSdkVersion
+        minSdk = 23
         targetSdk = flutter.targetSdkVersion
         versionCode = flutter.versionCode
         versionName = flutter.versionName

android/app/src/main/AndroidManifest.xml

@@ -1,5 +1,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
     <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
+    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
+    <uses-permission android:name="android.permission.WAKE_LOCK"/>
     <application
         android:label="sharedinbox"
         android:name="${applicationName}"