Making specifying a log file more convenient

[perrygreenfield]

Currently specifying a log file requires editing a .cfg file (and has the drawback that if one forgets that change to that file, one can be confused as why one is not seeing any output when running a task).

From the command line it should be possible to specify a log file as a command line option, and in Python, as a keyword argument to the method starting a pipeline step or pipeline.

Even better, it is useful to see both output to the log file in a terminal, and have that output go to a log file, so some sort of "tee" option should also be provided.