POC: Make possible to edit js in IDE and have changes reflected in running Nexus

Dev will have to define an env var NEXUS_RESOURCE_DIRS=comma separated list of root dirs to be searched for resources. If env var is defined and the js file is found starting from one of root dirs + path, it will be served, otherwise will fall back to standard way of working

Production way of running is minimal affected.

See a demo: http://screencast.com/t/wwXhGkBT