Sidebar redesign

[jvmespark]

Issue
closes #838

Photos

Additional Info
Impact of changes:

• Gave the user more room to breathe by simplifying the sidebar
• Optimized for the most common case: scrolling through courses
• Reduced filters down to a modal because it's not used often enough to have to always be on display
• Opened up new opportunities for developers to make course filters by giving it its own dedicated space

[jvmespark]

some older ideas that we can introduce to the new modal:
#777
#500

[EggyRepublic]

I think filter by department should be its own button due to how common its likely to be used. The dropdown could also be broken down for easier navigation like such: