Added editable attributes to workflow.py allowing editing of workflow

[tingard]

Added ['tasks', 'first_task', 'configuration'] to _edit_attributes in Workflow class in workflow.py

Seems to let you edit workflow objects as expected (tested on panoptes-staging.zooniverse.org)

[adammcmaster]

Looks good, just two small changes that'd be ideal.

1. Just a small style change, but could you put each attribute on a separate line? It makes it easier to read diffs later on.

2. Could you add display_name to the list too?

[adammcmaster]

See, e.g., project.py for what I mean in number 1.

[adammcmaster]

Thanks! This'll be in the next version, which should hopefully be released next week (depending on #69).