multiplatform: file structure (#2630)

* multiplatform: file structure

* apk file name

* more paths in sources

* lint issues and apk file name

apps/multiplatform/.gitignore

@@ -0,0 +1,20 @@
+*.iml
+.gradle
+/local.properties
+/.idea
+!/.idea/codeStyles/*
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties
+common/src/commonMain/cpp/android/libs/
+common/src/commonMain/cpp/desktop/libs/
+common/src/commonMain/resources/libs/
+android/src/main/cpp/libs/
+android/build
+android/release
+common/build
+desktop/build
+release