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-server/src/main/java/org/owasp/webgoat/StartWebGoat.java

@@ -22,6 +22,7 @@
  * projects.
  * <p>
  */
+
 package org.owasp.webgoat;
 
 import lombok.extern.slf4j.Slf4j;