[Feature] Notifications content on lock screen

[loochek]

Hello! My pull request adds a feature that I personally miss a lot.

I've added a setting to the "Notifications and Sounds" section that allows to disable hiding the contents of notifications on the lock screen.

It's my first contribution to the project (moreover - my first experience with Swift), so any criticism is strongly appreciated!

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
3 out of 5 committers have signed the CLA.

✅ zweeltow
✅ loochek
✅ walkline
❌ Mike Renoir
❌ overtake

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