small improvements & security update

changelog:
- added additional commands for nixos `gc` in fish
- changed default app to `mpv` for gif images in mimeapps.list
- added config for clamav-scanner
- added `fangfrisch` to clamav
- sandboxed some apps & added profiles through firejail
- changed vscode to vscodium
- updated README

nixos/flake.nix

@@ -17,6 +17,7 @@
         # ./disable-nvidia.nix
         ./opengl.nix
         # ./fingerprint-scanner.nix
+        # ./clamav-scanner.nix
         ./yubikey.nix
         ./sound.nix
         ./usb.nix