Update jQuery and replace deprecated things in the default admin theme

[evrifaessa]

When the admin_default theme was written, the latest version of jQuery was v1.7.1.

As of today, jQuery v3.5.1 is the latest version available, and the 1.x. and 2.x. versions no longer receive patches.
Developers who want to create new extensions mostly take the default layout that comes from the admin_default theme. There were some breaking changes in new jQuery version, and some functionalities of the latest jQuery does not exist in v.1.7.1. Hence, we need to update our jQuery and update it to comply with breaking changes.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. The resources of the BoxBilling team are limited, and so we are asking for your help. If this is a bug and you can still reproduce this error on the master branch, please reply with all of the information you have about it in order to keep the issue open. If this is a feature request, and you feel that it is still relevant and valuable, please tell us why. This issue will automatically be closed in the near future if no further activity occurs. Thank you for all your contributions.

[BelleNottelling]

I mentioned this in slack a while back, but we can use jquery-migrate to help with this process.
The lazy solution is it use the "production" version and update the bare minimum of what breaks.
The proper solution is to use the "development" version which will alert us in the browser console about which outdated functions are used, which should make it fairly straightforward to identify functions and plugins that need to be updated so we can use the latest jQuery version without the migrate library

[notbasetwo]

This needs to be split in to two steps - first migrating from 1.7.x to >=1.19 and then from >=1.19 to 3.x -- if using jquery-migrate that is.