Converted input placeholders to mat-label

Various style improvements

Updated translations

src/app/dialogs/set-default-admin-dialog/set-default-admin-dialog.component.html

@@ -7,7 +7,8 @@
     <div style="position: relative">
         <div>
             <mat-form-field color="accent">
-                <input type="password" (keyup.enter)="create()" matInput [(ngModel)]="input" placeholder="Password" i18n-placeholder="Password">
+                <mat-label i18n="Password">Password</mat-label>
+                <input type="password" (keyup.enter)="create()" matInput [(ngModel)]="input">
             </mat-form-field>
         </div>
     </div>