add git ignore file

+/env
+whatsup-ad0b7-firebase-adminsdk-6yhd1-2e4fcd728a.json
+
+*.iml
+.gradle
+/local.properties
+/.idea/caches
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+/.idea/navEditor.xml
+/.idea/assetWizardSettings.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+AppConfig.java
+libstreaming/build/*
+libstreaming/build/
+google-services.json