Merge branch 'learner' into 'dev'

.gitignore

benchmark/.gitignore

benchmark/build.gradle

.../java/de/tudresden/inf/st/eraser/benchmark/Benchmark.java

.../main/java/de/tudresden/inf/st/eraser/benchmark/Main.java

benchmark/src/main/resources/log4j2.xml

datasets/.gitignore

datasets/backup/activity_data.csv

datasets/backup/activity_data_readme.txt

datasets/backup/activity_model.eg

datasets/backup/preference_data.csv

datasets/backup/preference_data_readme.txt

datasets/backup/preference_model.eg

datasets/backup/test_data.csv

eraser-base/build.gradle

eraser-base/src/main/jastadd/Item.jrag

eraser-base/src/main/jastadd/Logging.jadd

eraser-base/src/main/jastadd/MachineLearning.jrag

eraser-base/src/main/jastadd/MachineLearning.relast

eraser-base/src/main/jastadd/Printing.jrag