Add fee rate display component

frontend/src/app/shared/components/fee-rate/fee-rate.component.html

@@ -0,0 +1,4 @@
+<ng-container *ngIf="rateUnits$ | async as units">
+  <ng-container *ngIf="units !== 'wu'">{{ fee / (weight / 4) | feeRounding:rounding }} <span *ngIf="showUnit" [class]="unitClass">sat/vB</span></ng-container>
+  <ng-container *ngIf="units === 'wu'">{{ fee / weight | feeRounding:rounding }} <span *ngIf="showUnit" [class]="unitClass">sat/WU</span></ng-container>
+</ng-container>