Use gradle to build kotlin files

Use `gradle test` to run the unit tests.

Kotlin/.gitignore

@@ -1,3 +1,25 @@
 .idea/
 out/
 *.class
+
+*.iml
+
+# Created by https://www.gitignore.io/api/gradle
+
+### Gradle ###
+.gradle
+**/build/
+
+# Ignore Gradle GUI config
+gradle-app.setting
+
+# Avoid ignoring Gradle wrapper jar file (.jar files are usually ignored)
+!gradle-wrapper.jar
+
+# Cache of project
+.gradletasknamecache
+
+# # Work around https://youtrack.jetbrains.com/issue/IDEA-116898
+# gradle/wrapper/gradle-wrapper.properties
+
+# End of https://www.gitignore.io/api/gradle