Update .gitignore

app/.gitignore

@@ -1 +1,32 @@
 /build
+
+# Created by https://www.gitignore.io/api/java
+# Edit at https://www.gitignore.io/?templates=java
+
+### Java ###
+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
+
+# End of https://www.gitignore.io/api/java
+