Use enhancements from Girder 2.0

[msmolens]

Once the plugin is converted to use Girder 2.0, investigate using the following enhancements:

• [x] UploadWidget: disallow multiple file selection (Create dataset view, Register metadata view). See https://github.com/girder/girder/blob/7dbab19fc4f37602e6784c1ea3ef7faa34cdf36a/clients/web/src/views/widgets/UploadWidget.js#L103-L104.
• [x] UploadWidget: use returned file ID to avoid lookups like https://github.com/ImageMarkup/isic-archive/blob/98ce4f001a47ce327acf06c94487caf32f96f1ea/web_external/Datasets/CreateDatasetView.js#L40-L54 (Create dataset view, Register metadata view). See https://github.com/girder/girder/blob/7dbab19fc4f37602e6784c1ea3ef7faa34cdf36a/clients/web/src/views/widgets/UploadWidget.js#L269.
• [ ] Investigate using girderEnable() in place of explicitly setting disabled attribute. See https://github.com/girder/girder/blob/7dbab19fc4f37602e6784c1ea3ef7faa34cdf36a/clients/web/src/utilities/jquery/girderEnable.js.
• [x] Verify that displaying modal dialogs in sequence is in fact no longer an issue and remove workarounds like https://github.com/ImageMarkup/isic-archive/blob/3fc6f15126dddb5a6186927806563ce9e655bb85/web_external/Featuresets/FeaturesetView.js#L39-L43. See https://github.com/ImageMarkup/isic-archive/issues/370.
• [ ] autoDescribeRoute, jsonParam