userArgs are optional parameters

These can be used in concrete implementation of a User.
Continuous user formats query with userArgs
Benchmark varies instances for a single user
Ignore result files
Removed whitespace
No text output for pipeline experiments
Show stderr per default for pipelining
Graceful shutdown on error during prepare
Removed some whitespace
Only log while benchmark has not been stopped
Remove stray print
Added op_name to eval
Mutiple plots for different runs