Remove jQuery and use vanilla JavaScript

[itismadness]

Vanilla JS has gotten to a point where most of the things that Gazelle was leaning on jQuery to provide can now be done there gaining some performance and also removing a dependency. This is especially important as Gazelles uses jQuery v1.8.2 and the path to upgrade this to the latest version would require a lot of work anyway in rewriting various parts of it that it's probably just as beneficial to remove it as much as possible.

This change should be communicated with users that old browsers (4+ years old at least) will lose various bits of functionality and that they either need to live with that or update their browser.