Code refactor

[mirmirmirr]

• refactored drag and drop by replacing it with a new library
  • gave toolbox and planner courses an ID for easier drag logic
  • gave each semester an ID for semester drag logic
• standardized course types (styling for their labels and badges)
  • added course credits to catalog courses
• added options to move to next semester and prev semester to the context menu (along with logic to exclude options for first and last semesters respectively)
• added bottom padding to the planner section to ensure all semester will be scrollable and viewable regardless of status of toolbox
• cleaned up color usage (converted everything to using tailwind names instead of hex)
• added no semester placeholder text