Upgrades HtmlUnit and it dependencies

Some major upgrades:
  /htmlunit
  /jetty
  /apache/commons
  /apache/http
  /xerces
  /tomcat/servlet-api

Fixes issue 7224

Change-Id: I36cc569c2926aa59ee7375e719b917d6d3681a43
Review-Link: https://gwt-review.googlesource.com/#/c/4323/
15 files changed