Customize payload params

[hoffm386]

The canvas_interface code currently hard-codes these values:

if options[:type] == "assignment"
  payload = {
    'assignment[name]' => name,
    'assignment[description]' => html,
    'assignment[submission_types][]' => "online_url",
    'assignment[grading_type]' => 'pass_fail',
    'assignment[points_possible]' => 1
  }
elsif options[:type] == "discussion"
  payload = {
    'title' => name,
    'message' => html
  }
else
  payload = {
    'wiki_page[title]' => name,
    'wiki_page[body]' => html,
    'wiki_page[editing_roles]' => "teachers" 
  }
end

To align with what DS is currently doing with the curriculum, it would be useful to be able to customize these through CLI arguments. In particular, the grading_type and points_possible args.

It would be nice to be able to attach an arbitrary dictionary of key/value pairs to be passed along to the API, although I'm not sure how complicated that would be