Build a command line executable for the JMX Extractor

With these changes, the an executable script is build for the jmx-extractor project and is bundled into jmx-extractor/target/jmx-extractor-1.0-SNAPSHOT-bin.zip when "mvn package" is run.  You can unzip the zip file and run the script in the bin directory.  Right now, the script runs the main() method of the org.jmxdatamart.Extractor.Main class, but we can change it to be whatever class has the main program.  This should make installing the extractor much easier.

I recommend that someone do the same thing for the loader.  We'll want a command line script for that, also.