Upgrade jquery version to 3.6

[stickz]

This pull request upgrades the jquery version to 3.6. There is a noticeable improvement in page loading speeds.

It also upgrades jquery.filedrop to the latest version. This fixes a bunch of bugs and makes it compatible with jquery version 3.6.

[Novik]

This is not such easy.
For example, only one moment:

Deprecation Notice: The jqXHR.success(), jqXHR.error(), and jqXHR.complete() callbacks are removed as of jQuery 3.0. You can use jqXHR.done(), jqXHR.fail(), and jqXHR.always() instead.

And what we have in the js/rtorrent.js?

For correct migration we should use jquery-migrate-plugin. Check this -
https://jquery.com/upgrade-guide/3.0/#jquery-migrate-plugin
https://github.com/jquery/jquery-migrate/#README

[stickz]

I'm still working on this jquery upgrade. It's going to take a few days to fully complete. I am using the jquery-migrate-plugin.

[stickz]

@Novik This pull request is ready for review again. I removed all the warnings from jquery migrate and resolved all the combability issues with JQuery version 3.6. Page loading speeds are slightly faster now which is great.

There is still some deprecated features used. They're not easily replaceable. It's not recommended, but it still works perfectly fine. An example of this is jQuery.type(), which is often used as $type() in the code. typeof doesn't work in every situation.

I came across some issues with error handling, while I was thoroughly testing this upgrade. The dbody container (which stores all the torrents) became null. This was due an issue with plugins not having adequate canChange permissions in plugins.ini. I had to clean up the chain reaction of errors. They were interfering with my ability to test this JQuery upgrade.