Use block count instead of oldest block for timespan selection

frontend/src/app/components/block-fees-graph/block-fees-graph.component.ts

@@ -69,19 +69,15 @@ export class BlockFeesGraphComponent implements OnInit {
           this.isLoading = true;
           return this.apiService.getHistoricalBlockFees$(timespan)
             .pipe(
-              tap((data: any) => {
+              tap((response) => {
                 this.prepareChartOptions({
-                  blockFees: data.blockFees.map(val => [val.timestamp * 1000, val.avg_fees / 100000000]),
+                  blockFees: response.body.map(val => [val.timestamp * 1000, val.avg_fees / 100000000]),
                 });
                 this.isLoading = false;
               }),
-              map((data: any) => {
-                const availableTimespanDay = (
-                  (new Date().getTime() / 1000) - (data.oldestIndexedBlockTimestamp)
-                ) / 3600 / 24;
-
+              map((response) => {
                 return {
-                  availableTimespanDay: availableTimespanDay,
+                  blockCount: parseInt(response.headers.get('x-total-count'), 10),
                 };
               }),
             );