BA Weber

This PR includes the following changes:

• Add support for multiple datasets
• Compute changes between current run and last run
• Compute execution order for Python execution frameworks
• Prepare retraining
• Add support for Python 3
• Resolve dataset dependencies (recursively)
• Read maven configuration, allows the definition of a custom local registry. Makes development in Docker containers easier.

Since the changes are based on some dependencies, the merge order is important:

graph TD;
  Datasets-->MNISTCalculator;
  emadl-maven-plugin-->MNISTCalculator;
  emadl-maven-plugin-->Datasets;
  maven-streamtest-->emadl-maven-plugin;
  CNNArch2X-->maven-streamtest;
  EMAM2Middleware-->maven-streamtest;
  EMADL2CPP-->maven-streamtest;
  CNNArch2X-->EMAM2Middleware;
  EmbeddedMontiArcDL-->EMADL2CPP;
  CNNArchLang-->EMADL2CPP;
  CNNArch2X-->EMADL2CPP;
  CNNArch2Gluon-->EMADL2CPP;
  CNNArch2X-->CNNArch2Gluon;