use progress spinner for imports

apps/desktop/src/app/tools/import/import-desktop.component.html

@@ -1,13 +1,19 @@
 <bit-dialog #dialog dialogSize="large" background="alt">
   <span bitDialogTitle>{{ "importData" | i18n }}</span>
   <ng-container bitDialogContent>
+    <div class="tw-relative">
       <tools-import
         (formLoading)="this.loading = $event"
         (formDisabled)="this.disabled = $event"
         (onSuccessfulImport)="this.onSuccessfulImport($event)"
         [onImportFromBrowser]="this.onImportFromBrowser"
         [onLoadProfilesFromBrowser]="this.onLoadProfilesFromBrowser"
+        [class.tw-invisible]="loading"
       ></tools-import>
+      <div *ngIf="loading" class="tw-absolute tw-inset-0 tw-flex tw-items-center tw-justify-center">
+        <i class="bwi bwi-spinner bwi-spin bwi-3x tw-text-primary-600" aria-hidden="true"></i>
+      </div>
+    </div>
   </ng-container>
   <ng-container bitDialogFooter>
     <button