update proguard rules for androidx library, fixes #810 (#811)

# Keep our own classes to keep stack traces readable. 

-keep class org.dmfs.** {*;}

# Allow obfuscation of android.support.v7.internal.view.menu.**

# to avoid problem on Samsung 4.2.2 devices with appcompat v21

# see https://code.google.com/p/android/issues/detail?id=78377

-keep class !android.support.v7.internal.view.menu.**,android.support.** {*;}

-keep class androidx.** {*;}

# this is required to keep the Annotations for retention-magic and to keep the line numbers n stack traces

-keepattributes *Annotation*,SourceFile,LineNumberTable

    @org.dmfs.android.retentionmagic.annotations.* <fields>;

    private long mId;

}

# same for support library Fragments

-keepclassmembers class * extends androidx.fragment.app.Fragment {

    java.lang.String TAG;

    @org.dmfs.android.retentionmagic.annotations.* <fields>;

    private long mId;

}

 No newline at end of file