Improved code uniformity across tasks

[laurencejackson]

Is your feature request related to a problem? Please describe.
When developing a web interface for Hazen we have come across multiple issues caused by tasks having variable expected inputs.

Describe the solution you'd like
Refactor the hazen library to use an object oriented approach

Describe alternatives you've considered
Modifying the existing tasks to all accept identical inputs, this approach might be simpler in the short term but the OO approach will make Hazen easier to maintain in the long term.

[tomaroberts]

@laurencejackson – is this still applicable given your re-factoring and the HazenTask class?

[laurencejackson]

Resolved by #266