Download Refactor (#483)

# Added
- New: Cards when processing a download shows a spinner for the progress of the download

# Changed
- Changed: Downloads now always take the backend filename and are streamed in a more optimal manner, reducing the javascript processing that was needed previously.
==================================

* Started refactor of downloader to be more UX friendly and much faster.

* Completed refactor of Volume download to use a new mechanism. Downloads are streamed over and filename used exclusively from header. Backend has additional DB calls to get the Series Name information to make filenames nice.

* download service has been updated so all download functions use new event based observable. Duplicates code for downloading, but much cleaner and faster.

* Small code cleanup

UI/Web/src/app/shared/_providers/saver.provider.ts

@@ -0,0 +1,10 @@
+import {InjectionToken} from '@angular/core'
+import { saveAs } from 'file-saver';
+
+export type Saver = (blob: Blob, filename?: string) => void
+
+export const SAVER = new InjectionToken<Saver>('saver')
+
+export function getSaver(): Saver {
+  return saveAs;
+}