#2743: user's availability calendar now reflects RSVP'd meetings

[gcooper407]

Changes

When users RSVP to a meeting (i.e. provide their availability for a design review meeting), as soon as the meeting time is selected by the host, all attendee's availability calendars get updated to reflect the meeting, i.e. the time block of the meeting shows as no longer available.

Notes

It seems that availability dates stored in the db are typically off by ~1 day, so as a temporary measure until this behavior is fixed, I offset the date/time by 1 day to account for the error, but once resolved, that logic can simply be removed (I left in the code that should work as a comment).

I'm putting up this PR now just to have progress and so I can move onto other ticket, but might want to wait on merging this until that date bug gets resolved.

Screenshots

Here's a walkthrough of the full process, just so it's clear when the availability gets adjusted and how it appears to the user:

demo.mp4

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Closes #2743

[superhvarn]

LGTM