Fat jar is not properly assembled with sbt

"sbt assembly" with the current build properties does not actually create a fat jar with all required dependencies (at least spark dependencies seem to be messed up).

When running serene via "bin/serene-start", training of models fails with the error:
Error while instantiating 'org.apache.spark.sql.internal.SessionState'

Running serene via "sbt run" does not have these issues.