Index meetings by semester

[WhiteHoodHacker]

Changes

• /meetings/ no longer displays all meetings by default
• New /meetings/[...semester]/ routes are added which serve as index pages for meetings now
• An additional /meetings/all/ route is added to render all meetings
• Schedules can now be added on a per-semester basis, and allows future content to be rendered on meeting semester index pages
• Added new navigation for navigating between semester index pages
• Add new "seminar" meeting type

Fixes

• Fixes Implement meetings index pagination or infinite scroll #121
• Fixes Past meetings remain in upcoming on meetings page if site was built in past #240

TODO

• Add improved meeting type badges
• Update Meeting sidebar to support new semester navigation
• Update meeting controls (likely don't need filter by type anymore)
• Improve component for meeting type stack
• Add clickable tooltips to learn about meeting types
• Replace meeting tags on meeting index pages with meeting type badges