updates jQuery references in the backend to version 4.0.0

[krHERO]

Description, Context and related Issue

Updates jQuery references in the backend to version 4.0.0, consistent with
the frontend update, see Edirom-Online-Frontend: PR226).

Two separate backend files loaded different outdated jQuery versions:

• index.xql referenced resources/jquery/jquery-2.1.3.js (local file that did
  not exist — jQuery was silently not loading in this context)
• getAudioPlayer.xql referenced resources/js/jquery-2.1.4.min.js

Both are replaced with a CDN reference to 4.0.0.

Refs Edirom/Edirom-Online-Frontend#187

How Has This Been Tested?

• Docker container rebuilt with updated backend
• Manual test: AudioPlayer opened and functional

Types of changes

• Improvement

Overview

• I have performed a self-review of my code, according to the style guide
• I have read the CONTRIBUTING document.
• All new and existing tests passed.

[peterstadler]

I think JQuery should really be removed from the backend rather than updated.
The file index.xql could easily be removed completely since it's not needed anymore?
And the Javascript in data/xql/getAudioPlayer.xql should be rewritten to get rid of JQuery.

Just my 2c …

[krHERO]

I think JQuery should really be removed from the backend rather than updated. The file index.xql could easily be removed completely since it's not needed anymore? And the Javascript in data/xql/getAudioPlayer.xql should be rewritten to get rid of JQuery.

Just my 2c …

what about updating for this release, but prepare a new issue to get rid of JQuery completely until the next one?

[daniel-jettka]

This needs some testing with edition data that uses the old getAudioPlayer.xql (e.g Freischütz). So I think it's good to do it for the release 1.5.0 which is about reducing dependencies and cleanup.