First attempt at CLI

[diegostruk]

• Adds a CLI module to interact with the pyworkflow module: making CLI a module for now, but we can consider making it its own service in the future. For now I think this might be sufficient, but this is open to discussion.
• Adds a execute_workflow which gets the order of node execution and executes it at once. This attempts to cover the: 'Provides a CLI with support for batch execution of workflows' requirement.