make logback instlation script Jetty 9.x compatible

make logback instlation script Jetty 9.x compatible

in the script:
- download logback libraries to lib/etc instead of lib/logging (as OPTIONS parameter no nonger works in start.ini)
- in start.ini, add logging module instead of specifying OPTIONS=logging
- set output directory to ${jetty.base} instead of ${jetty.home} to make it more Jetty 9.x directory structure friendly