New calendar implementation

[ByAgenT]

This PR adds new calendar to the main page of the website. This removes dependency on StyledCalendar, but would require daily rebuild of a website, since event data is fetched at build time.

Remaining to-do:

• Add scroll to limit number of events currently rendered on the page (max 4-6 I think)
• Add necessary secrets to CI process to fetch calendar events at build time
• Add "Add to my calendar" button in the modal (if that's possible)