Optimization of http calls on the Download and API tabs + small css fix

...et-detail/components/dataset-api/dataset-api.component.ts

...onents/dataset-downloads/dataset-downloads.component.html

...onents/dataset-downloads/dataset-downloads.component.scss

...mponents/dataset-downloads/dataset-downloads.component.ts

...ource-download-item/resource-download-item.component.html

...ource-download-item/resource-download-item.component.scss

src/app/dataset-detail/services/resources.service.ts