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/admin/manage-system/manage-system.component.html

@@ -16,7 +16,7 @@
               <button ngbDropdownItem (click)="clearCache()" [disabled]="clearCacheInProgress">
                 Clear Cache
               </button>
-              <button ngbDropdownItem (click)="downloadService.downloadLogs()">
+              <button ngbDropdownItem (click)="downloadLogs()" [disabled]="downloadLogsInProgress">
                 Download Logs
               </button>
               <button ngbDropdownItem  (click)="checkForUpdates()" [disabled]="hasCheckedForUpdate">

UI/Web/src/app/admin/manage-system/manage-system.component.ts

@@ -1,7 +1,8 @@
 import { Component, OnInit } from '@angular/core';
 import { FormControl, FormGroup, Validators } from '@angular/forms';
 import { ToastrService } from 'ngx-toastr';
-import { take } from 'rxjs/operators';
+import { asyncScheduler } from 'rxjs';
+import { finalize, take, takeWhile, throttleTime } from 'rxjs/operators';
 import { DownloadService } from 'src/app/shared/_services/download.service';
 import { ServerService } from 'src/app/_services/server.service';
 import { SettingsService } from '../settings.service';
@@ -22,6 +23,7 @@ export class ManageSystemComponent implements OnInit {
   clearCacheInProgress: boolean = false;
   backupDBInProgress: boolean = false;
   hasCheckedForUpdate: boolean = false;
+  downloadLogsInProgress: boolean = false;
 
   constructor(private settingsService: SettingsService, private toastr: ToastrService, 
     private serverService: ServerService, public downloadService: DownloadService) { }
@@ -87,4 +89,16 @@ export class ManageSystemComponent implements OnInit {
     });
   }
 
+  downloadLogs() {
+    this.downloadLogsInProgress = true;
+    this.downloadService.downloadLogs().pipe(
+      throttleTime(100, asyncScheduler, { leading: true, trailing: true }),
+      takeWhile(val => {
+        return val.state != 'DONE';
+      }),
+      finalize(() => {
+        this.downloadLogsInProgress = false;
+      })).subscribe(() => {/* No Operation */});
+  }
+
 }