some backend fixes and add android app

android/gradle.properties

@@ -0,0 +1,9 @@
+org.gradle.jvmargs=-Xmx2g -Dfile.encoding=UTF-8
+org.gradle.caching=true
+org.gradle.parallel=true
+org.gradle.configuration-cache=true
+
+kotlin.code.style=official
+
+android.useAndroidX=true
+android.nonTransitiveRClass=true