Fix kpoland modal backdrop errors

[klpoland]

Not sure what happened here, but seems some previous work got lost during rebasing. Restored/recreated what I could and did some extra refactoring to remove redundant code. Modals are opening and lists refresh properly on changes now.

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
gateway/sds_gateway/static/js/actions/__tests__/DownloadActionManager.test.js	41% smaller
gateway/sds_gateway/templates/users/partials/web_download_modal.html	36% smaller
gateway/sds_gateway/static/js/actions/DownloadActionManager.js	19% smaller
gateway/sds_gateway/static/js/file-list.js	0% smaller
gateway/sds_gateway/templates/pages/home.html	Unsupported file format
gateway/sds_gateway/templates/users/components/dataset_list_modals.html	0% smaller
gateway/sds_gateway/templates/users/components/dataset_list_table.html	Unsupported file format
gateway/sds_gateway/templates/users/dataset_list.html	0% smaller
gateway/sds_gateway/templates/users/file_list.html	0% smaller
gateway/sds_gateway/templates/users/files.html	Unsupported file format
gateway/sds_gateway/templates/users/partials/captures_page_table.html	Unsupported file format
gateway/sds_gateway/templates/users/partials/my_datasets_tab.html	Unsupported file format
gateway/sds_gateway/templates/users/partials/search_published_datasets_tab.html	Unsupported file format
gateway/sds_gateway/templates/users/published_datasets_list.html	0% smaller
gateway/sds_gateway/templates/users/search_datasets.html	Unsupported file format
gateway/sds_gateway/users/views.py	0% smaller

[lucaspar]

thanks