Changed Launcher properties to overrides
Add support for picking up configuration properties from some few select environment variables, as well as few select legacy environment variables.
Add example usage of new configuration to enable the request log, which _augments_ the configuration to add features instead of _replacing_ the jetty.xml file
Merge pull request #245 from sonatype/NEXUS-6027-simplify-jetty-integration

REVIEW: [NEXUS-6027] simplify jetty integration
Merge branch 'master' into NEXUS-6027-remove-appcontext
Merge pull request #253 from sonatype/NEXUS-6027-remove-appcontext

REVIEW: [NEXUS-6027,NEXUS-5279] remove appcontext
Merge branch 'master' into NEXUS-6027-testsuite-cleanup