Add feature to add and remove assignments

[CHR-onicles]

Bot should be able to add assignments with the following info:

• Course
• Description
• Due date

It should also be able to remove assignments with a command. Data would be persisted through a deployed database.

It should either broadcast to relevant persons through dm or groups that an assignment has been added, while expired assigments(assignments whose due dates have passed) should be removed unnoticed (or not?).