Update or replace jQuery

Current GUI jQuery version is 1.9.0, which is 9 years old.. This should either be updated or replaced. The latest version is 3.6.0 released in 2021.

jQuery versions prior to jQuery 3 are known to have a bunch of security vulnerabilites, and jQuery is in general seen as superseded by newer JS features and other frameworks, so at some point a decision should be made whether to stick with its legacy or to replace it.