[web] Calendar scrolling

Summary:
ENG-1678
This diff adds a scrollbar to the calendar if it's too big vertically.

Test Plan: Test if calendar can be scrolled. Check if there is no scrollbar when it's not needed (the screen is high enough).

Reviewers: tomek, atul, abosh, ginsu

Reviewed By: tomek, ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5472