Calendar reminder for airdrop claim deadline

[LefterisJP]

Abstract

Now with 1.33.0 we have the calendar feature and the ability of rotki to add calendar reminders for events that users perform on-chain. One such reminder would be airdrop claim deadlines.

Motivation

Make sure users with eligible addresses do not miss airdrops.

Specification

• Check airdrops user's addresses are eligible for.
• Find the ones that user has not claimed yet (or rotki doesn't know whether user has claimed)
• Add a calendar reminder at the expiration of the airdrop
• Make sure user is notified

Caveat: Since some airdrops may not have the ability to decode the claim event yet, we may have false positive reminders for airdrops that have been claimed, but that's fine.