Code style (#696)

* Remove Guava dependency from WebGoat

* Add Checkstyle to the project with very basic standards so we have a
style across lessons. It does not interfere with basic Intellij formatting

webgoat-container/src/main/java/org/owasp/webgoat/WebGoat.java

@@ -28,6 +28,7 @@
  * @version $Id: $Id
  * @since October 28, 2003
  */
+
 package org.owasp.webgoat;
 
 import org.owasp.webgoat.session.UserSessionData;