Fix CalibMon and improve warnings on testbench

This MR fixes 2 things:

• CalibMon was not properly working as it tried to write to the MBM Buffer even though none was registered, as described in #101. Reason being that the default OutputType is 'Online' and has to be overwritten for CalibMon (which is a monitoring algorithm, but set up exactly the same way as HLT2)
• When running the testbench with --measure-throughput=-1 the testbench crashed after processing all files. Running with negative numbers is actually not supported. For processing all files in a given directory one has to specify --measure-throughput=0. Clarified the argparser to have meaningful error messages.