Improve Ewoks task documentation with input/output typing and description

Task inputs and outputs were added in !56 (merged)

@tvincent expressed the concern that it might not enough without input descriptions and typing. To improve this, we could add docstrings to task classes that would describe inputs/outputs type and purpose (e.g. with :param:)

This docstring could then be parsed using standard autodoc processes to generate the task entry in the task catalog.