Report mean error in maven-memory-allocation-{date-time}.csv file

[jeanbisutti]

When MvnValidateAllocationByMaven3VersionTest is executed, results are exported into a maven-memory-allocation-{date-time}.csv file. You can consult an example here.

The goal of this issue is to add an Error column in the CSV file giving the mean error for a given confidence level. The confidence level may be given by the user with the help of maven-bench.properties file. To compute the error mean, Apache Commons Math (https://commons.apache.org/proper/commons-math/) could be useful.