Major refactor in core algorithm and structures

[benny-n]

Sorted by priority:

• Modify CourseBank to hold its own list of courses (or a predicate which determines if the course belongs to said bank)
• Refactor the way we handle course replacements - the main obstacle is that a replacement can cause a side effect, for example replacing a course with a course with higher credit can lead to a different overflow calculation - POTENTIAL SOLUTION: always access courses through a dedicated method of CourseBank, which will either return the actual course or a replacement for it.
• After modifying CourseBank, some rules might become redundant (malag, sport, elective, etc.) - Remove them.