GroupedSubmission 'submissions' key:value deleted

[Thetwam]

Describe the bug

In #280 we added the first instance of nesting a list of one type of object inside another. While this generally works well, there is a small side effect: The 'submissions' key:value pair is removed from the attributes dict. This is potentially misleading, since one of the uses of calling attributes is to see what data was originally used to create the object (via .to_json()).

'submissions' being removed may give the (incorrect) impression that submissions were never returned from Canvas.

To Reproduce

Steps to reproduce the behavior:

1. Create a GroupedSubmission object with nested submissions
2. Print the attributes of the created object (print(grouped_submission.attributes))
3. Observe that there is no 'submissions' key:value pair

Expected behavior

'submissions' should be visible in the printed attributes, to assist in debugging.

Environment information

• Python version (python --version)
  3.7+

• CanvasAPI version (pip show canvasapi)
  0.14.0

Additional context

This is somewhat related to #56, as we'll need to be careful about deleting keys in the future.

[Thetwam]

canvasapi/canvasapi/submission.py

Lines 182 to 191 in 3ef34a8

	try:
	self.submissions = [
	Submission(requester, submission)
	for submission in attributes["submissions"]
	]
	del attributes["submissions"]
	except KeyError:
	self.submissions = list()
	super(GroupedSubmission, self).__init__(requester, attributes)

The issue lies here. We're deleting the 'submissions' key before it's passed off to CanvasObject.__init__(). We could call super() first, then override self.submissions after, although that does mean a little bit of extra processing.