Minor UI improvements

- Fixed DSO edit menu sometimes displaying underneath header based on header z-index
- Fixed accessibility issue on request a copy page

src/app/item-page/bitstreams/request-a-copy/bitstream-request-a-copy-page.component.html

@@ -1,5 +1,5 @@
 <div class="container">
-    <h3 class="mb-4">{{'bitstream-request-a-copy.header' | translate}}</h3>
+    <h1 class="mb-4">{{'bitstream-request-a-copy.header' | translate}}</h1>
     <div *ngIf="canDownload$|async" class="alert alert-success">
         <span>{{'bitstream-request-a-copy.alert.canDownload1' | translate}}</span>
         <a [routerLink]="getBitstreamLink()">{{'bitstream-request-a-copy.alert.canDownload2'| translate}}</a>

src/app/shared/dso-page/dso-edit-menu/dso-edit-expandable-menu-section/dso-edit-menu-expandable-section.component.html

@@ -1,6 +1,6 @@
 <div class="dso-button-menu mb-1" ngbDropdown container="body" placement="bottom-right">
     <div class="d-flex flex-row flex-nowrap"
-         [ngbTooltip]="itemModel.text | translate">
+         [ngbTooltip]="itemModel.text | translate" container="body">
         <button [attr.aria-label]="itemModel.text | translate" [title]="itemModel.text | translate" class="btn btn-dark btn-sm" ngbDropdownToggle [disabled]="section.model?.disabled">
             <i class="fas fa-{{section.icon}} fa-fw"></i>
         </button>