Update README.md
Update the Codenvy SDK launcher to be more resilient

* Handle situation where user has not ran 'mvn clean install' or ran 'mvn clean'
* Handle situation where Tomcat download fails
* Updated Tomcat download url to use Apache Archive URL vs. Apache Mirror URL to
  avoid the script failing when Tomcat's version updates (Apache Mirror hosts
  only host the latest version while the Apache Archive host hosts all versions)
* Various code/interface cleanups