Commandline arguments

[jmafoster1]

Behave supports the passing of commandline arguments with -D variable=value. These can be pulled out from the context.config.userdata dictionary. This is quite handy for passing in things that we want to change in experiments, like the CSV file to use for observational data, the number of data points to sample, and the adjustment set. Currently, this is done in the environment.py file of each set of feature files. It would be much better if this was part of the "tool" so that it would work universally for everything rather than having to duplicate the code in every environment.py file.