feat(nix): nix and back again

I tried Nix, but it had too many downsides so I removed it.

1. Didn't like that all files are immutable and simple config changes
need a complete rebuild.
2. Setting up a new Mac didn't work as smoothly as promised. Not worth
the effort.
3. It sucked a lot to always have to type in the password twice on each
darwin-rebuild
4. It solves problems I never had.

.config/fish/functions/unquarantine.fish

@@ -0,0 +1,5 @@
+function unquarantine --description "Manually remove a downloaded app or file from the quarantine"
+    for attribute in com.apple.metadata:kMDItemDownloadedDate com.apple.metadata:kMDItemWhereFroms com.apple.quarantine
+        xattr -r -d "$attribute" $argv
+    end
+end