Add settings for DEBUG and INSTRUMENT and INSTRUMENT_PREFIX

	modified:   analyzer/analyzer.py
	modified:   horizon/horizon-agent.py
	modified:   horizon/worker.py
	modified:   settings.py.example
	modified:   webapp/webapp.py
Add settings for DEBUG and INSTRUMENT and INSTRUMENT_PREFIX:
DEBUG: Only add debug output if requested (shrinks our log files!)
INSTRUMENT: send our stats to Graphite
INSTRUMENT_PREFIX: The starting position in the Graphite tree where data should be sent (in case "skyline" doesn't fit in your layout)

Added rotating file handlers for logging, a start towards not destroying old log files