Ensure DispatcherServlet is available in a deployed WAR

The DispatcherServletAutoConfiguration had a condition on it that
meant it wasn't used at all if there was no EmbeddedServletContainerFactory.
It's amazing that any WAR ever deployed.

Also added some info logging to servlet and filter registrations.
Try to make Jetty scan TLDs in nested JARs

Jetty apparently does it differently (different version of
Jasper maybe), so you need a unique jarFileURL for each
nested JAR (previously they were all set to the parent
archive URL).

Also added the root of the main archive as a valid
document root.

For gh-367