Implementation of logistic regression in stratosphere

Created by: markus-h

This is the full implementation of logistic regression in stratosphere. This pullrequest also includes Testcases and sample datasets for theses testcases. We had to change the pom to use 0.5.1 version, because some bugfixes were only done for this version. (for example https://issues.apache.org/jira/browse/FLINK-905)

For now we are using the ArrayRealVector class from commons-math3 from the org.apache.commons library for vector calculations. If needed we can replace the used class by an own implementation.

For overview reasons we merged all our commits into one, altough we all worked on this implementation.