GUI: make all error message non-auto-disapearing

Currently, "toasts" for error messages are set to auto-disappear after a set number of seconds.

It would probably be better that these messages do not auto-disappear, and have to be manually closed by the user (there is already a button on the toasts for that), so we are sure the user is aware of the error (e.g. if they go away from their computer, they might not see the error before it has disappeared).