Upload views: Javascript tests + modernizing

[StephenChan]

Tests should mostly be QUnit, with potentially a few LiveServerTestCases. Modernizing means:

• Using ES6 classes and syntax
• Not relying on jQuery too much, including using fetch instead of jQuery.ajax

5 files that I'd put under this issue:

• UploadAnnotationsCPCHelper.js
• UploadAnnotationsHelper.js
• UploadImagesHelper.js
• UploadMetadataHelper.js
• LabelsetImport.js

I'm very much hoping that ES6 classes could help to reuse code between most of these JS files.