BA Weber

This PR includes the following changes:

• Add retraining_type with values ignore, automatically or manually
• Add custom retraining_optimizer

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;