Add Android app implementation with core features

Co-authored-by: Kenearos <86194771+Kenearos@users.noreply.github.com>

android-app/app/proguard-rules.pro

@@ -0,0 +1,9 @@
+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in ${sdk.dir}/tools/proguard/proguard-android.txt
+
+# Keep data classes
+-keep class com.dienstplan.nrw.model.** { *; }
+
+# Keep ViewBinding classes
+-keep class com.dienstplan.nrw.databinding.** { *; }