Increase targetSdk to 30 and support signature scheme v2 (#1413)

[This removes the warning that this app may not be compatible because it
was developed for an older
android-version.](https://developer.android.com/about/versions/10/behavior-changes-all#low-target-sdk-warnings)
Also, this adds support for signature scheme v2 and v3 [which reduces
the attack surface along with other
benefits](https://source.android.com/docs/security/features/apksigning#v1).
Lastly this adds 64-bit support for the APK, so this app can be
installed on 64-bit-only hardware.

android/build.gradle

@@ -70,7 +70,7 @@ android {
 
     defaultConfig {
         minSdkVersion 19
-        targetSdkVersion 26
+        targetSdkVersion 30
         versionCode 22
         versionName "1.52-dev"
     }