Notesnook Desktop v3.0.21

This is a hotfix release fixing a bunch of issues with v3.0.20:

1. Fix issue where app lock always gave "Wrong password" error
2. Fix issue where editor margins weren't saved across sessions
3. Fix issue where images flickered and disappeared after load
4. Fix issue where headings appeared jumbled together

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Read Notesnook v3.0.20's release notes on Notesnook's blog

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Full Changelog: v3.0.20...v3.0.21