feat: consider weight in score calculation

[mariajgrimaldi]

Description

This PR changes what is considered the final score for the student. Before these changes, we considered the raw score as the final score for the student without considering the weight configured. Now, we calculate the final score based on the weight configured in studio. This change has a downside: after calculating the new score, we could get numbers like 5.3 which cannot be saved in the submissions API so we decided to round to the nearest integer.

How to test

0. Configure grading in your course as follows:
   
1. Install this branch and add the xblock to your course
2. Configure your mindmap with your preferred weight. For this test, we're using 10 (the default):
   
3. As a student, submit a mindmap
   
4. As course staff, go to the component in the LMS and grade the submission:
   
5. As a student, check out your grade:
   
   From the progress page:
   
   Since the problem weight is 100, then our grade is 50. If the problem weight is 50, then our grade would be 25% and so on. Now, the subsection grade is our weighted score.

[BryanttV]

@mariajgrimaldi, it works fine except for one test case. I configured a component like this:

• weight=10 (default)
• maximum_score=100 (default)

As an instructor, I scored the submission with 5, but the submissions list doesn't show me the Raw score, should show me 5/100

[BryanttV]

LGTM!

[mariajgrimaldi]

I'll be merging this since all comments have been addressed!