REVIEW: NEXUS-6153 inline jetty config examples

Following on @jdillon work to allow jetty config files as app parameters, this pull:

- makes any useful example jetty config as valid for the app parameter use case
- makes request logging enabled by default
- makes the rotated log file names for request.log and nexus.log be consistently named
- removed any out of date examples as noted
- uses logback-access request log impl so that request logs are rolled gzipped ( Jetty request log impl can't do this )
- further improved JMX config
- replaced deprecated ${property} notation with xml <Property />
- removed duplicate jetty.xml

https://issues.sonatype.org/browse/NEXUS-6153