Grader enhancements

* Plotting of chart images can be turned off via optional parameter "-n"
* Failed SLAs show up Summary Page
* Summary Stats Tables on Metric Pages are color coded based on SLA and the SLA rule applied is available via tooltip
* Enhancements to Jmeter Metric so that Important Sub-Metrics, SLA and CDF plotting work correctly
* I have not figured a good unit test for reporting, so there are no unit tests in this pull request. I have tested it manually.