Extract results and run multiple scenarios

[willu47]

Adds functionality to:

• specify one or more data packages in a scenarios.csv file - this allows you to run the same parameter sample for one or more scenarios e.g. one data package containing a model which forces in the interconnector, and another which optimises
• a "reduce" step which extracts results from a bunch of successful model runs for each scenario
• a more generalised formulation which makes the workflow OSeMOSYS model agnostic - you configure which model you use, input parameters to sample and results to extact

Improves documentation

• more specific info in the readme about setting up the configuration
• docstrings in the scripts to describe what's happening

[abhishek0208]

@willu47 This looks good. After help from the "coach" I'm still running into another error KeyError: 'Only a column name can be used for the key in a dtype mappings argument.'. Snakemake log attached 2020-11-09T185054.304084.snakemake.log

[willu47]

My bad - try the latest version of http://github.com/OSeMOSYS/simplicity