Move Async and Comet examples from JSP examples page to Servlets examples page,
like it have already been done in Tomcat 8.

Merged r1518578, r1518581, r1518589 from tomcat/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1633489 13f79535-47bb-0310-9956-ffa450edef68