Allow users to visualize subtasks on Calendar and get notifications

[drozd-A]

Describe the solution you'd like
Allow users to visualize subtasks on the Calendar and setup subtask notifications to remind them of deadlines.

Describe Possible Solutions
Use email notifications that have already been implemented for the subtasks and use pre-made functions to add calendar events for subtasks with a distinction between subtask and assessment.

Additional context
N/A