Important fixes (v2)

[WarningImHack3r]

(From elmerfds#305. No other changes were made apart from copying this previous PR.)

This PR does

• Fix ambigous (and dangerous) behavior during uninstall
• Global fix for shell formatting
• Small refactors
• Fix unhandled cases in yes/no questions
• Handle uninstallation for certbot via snap or apt

Some notes

• These changes should probably be applied to CentOS script too. You can use ShellCheck to look for stuff to change, and/or copy the ones I made.
• There seem to be some other things to remove, such as crontab entry as I've seen, but I didn't dig enough into the script to be sure.
• And please, never delete folders that may contain anything other than the targeted program, such as important folders like /var/www. If you cannot be sure it won't affect anything else, let the user do it themselves.
  I've lost all my existing websites and certbot certificates because of this script, while it was vaguely mentioning "Web folder" and "Letsencrypt folder". (Fortunately, I had some recent backups)