FELIX-3956 - JAAS Support bundle should have optional dependency on Servlet API

Using ServiceFactory to register the WebConsolePlugin to avoid direct dependency on Servlet API. Also using DynamicImport-Package (without using wildcards) for the servlet api.

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1456909 13f79535-47bb-0310-9956-ffa450edef68