Link userstory up to assignment submission to the new API

Due to two databases with different data, the website might throw errors where the old API is still used, for example when a search is done for something that doesn't exist in the new API v2 database.

We decided to follow the user story and merge the new API connection in parts to avoid a huge mr that connects the entire API at once.

This is the first part. We follow the userstory for manual testing convenience (hard to test a review if you can't create or enter a course). This pr connects the following to the new API (all student view):

• Courses overview (both tabs and filters)
• Session check
• Create course
• Assignments overview, only the first two tabs (other tabs need a rubric for convenient manual testing):
  • Open for enrolment
  • Ready for submission
• Assignment overview, only the first two tabs:
  • Assignment information
  • Submission