naarad enhancements / bug fixes

1. matplotlib plotting is now thread safe
2. switch from multithreading to multiprocessing
3. scaling of png display based on user's screen resolution
4. improved error handling for calculate_stats
5. bugfix for metric.collect
6. bugfix for protection metric in ProcZoneInfoMetric
7. enhance client side charting to support discovery and data from a different naarad report