add testOneRegi option to refactored start scripts

testOneRegi runs are useful for fast development iterations ("do these changes break the model, or does it still run"), so setting them up should be fast as well

supplying the parameter --testOneRegi to start.R will ignore any scenario_config file provided and modify the default configuration to start a testOneRegi run in the directory output/testOneRegi with no output processing

the old oneRegi.R script and oneRegi.cfg configuration are deleted

existing output/testOneRegi directories are overwritten