Add task definitions for duty as alternative command runner

[dalito]

Adds a duties.py tasks file for the duty command runner.

The added commands should match the current makefile. The code for the tasks in duties.py may be made nicer given the power of Python but I first wanted to closely follow the makefile.

Closes #120

[pkalita-lbl]

Not to derail this but I've had my eye on Task as a cross-platform alternative to make, but I've never really had a good excuse to use it. I've never seen duty before. It seems interesting, but I'm just mulling over the tradeoffs of tasks defined via code vs configuration.

EDIT: Whoops! I just saw in this issue that you already did consider Task as an option.

[dalito]

@pkalita-lbl - Task or just are probably a better choice for someone who does not know/like Python or for developers who want one tool for all their projects (also Python-free ones). The preference for duty here is only driven by the desire to be compatible with the installation process and to cause least challenges for newcomers.