Fix assignment/assessment identifier mismatch issue

[substance9]

#18
There is an identifier mismatch problem in the generated assessment_meta.xml, which will lead to an issue that Canvas ignores the quiz description, quiz options, and questions titles. The root cause of the problem is in the qti.py, when instantiating the assessment_meta and assessment. Simply change the following lines will fix the issue:

line 39 in qti.py:
From: assignment_identifier=self.assessment_identifier,
To: assignment_identifier=self. assignment_identifier,

line 49 in qti.py:
From: assessment_identifier=self.assignment_identifier,
To: assessment_identifier=self. assessment_identifier,

[JeffFessler]

@substance9 I am thrilled about the possibility of getting question titles working - and it does!
But I am confused about the PR itself because there are 100s of changed lines of code
whereas the PR describes only a couple very small changes.
Perhaps the PR may be more likely to be accepted if it focuses on just one issue at a time.