Make pie chart plotting ratio of delivered messages

Script can be called like this: python toolkit/reportSummary/privateMessageAnalysis.py /reports/realisticScenario_DeliveryProbabilityReport.txt reports/DeliveryProbability.png

It generates images like this:

We do not need a seperate script for delay as Britta's Script (in !130 (merged)) includes that. That one can be called with:

python toolkit/reportSummary/delayDistributionAnalysis.py reports/messageDelayAnalysis.txt ONE_TO_ONE 0 reports/PrivateMessageDelay.png