Grouping

[LeoLee5566]

Group similar courses together(as one node) thus the layout won't be very messy. Grouped courses will be displayed only when the student clicks the integrated node.

[LeoLee5566]

Known bug: If a course belongs to more than 1 group(that's the situation in Exclusion.csv), its lines will be messed when one drags that course and uses the reset button. Not sure whether this duplicate is what we intend to do, I'd rather change the Exclusion file to fix the lines.