Update WarLauncher to remove the root of the war from the classpath

Previously, WarLauncher included its root on the classpath. It also used
a filtered version of its root archive to hide both the WEB-INF and
META-INF directories. This meant that files in WEB-INF and META-INF
could be found by the classloader (as they were on the classpath) but
could not be read as the filtered archive was hiding them.

This commit updates WarLauncher to remove the root of the war file from
the classpath. It also removes the filtering of the archive, thereby
allowing files in META-INF and WEB-INF to be accessed via the
ServletContext.

Closes gh-1792