UI/UX - New component for difficult adjustment. (#602)

* Add next difficulty blocks.
Add next difficulty target date.
Add next difficulty total progress.
Add ajustment difficulty avg min per block.

* Fix typo.

* Trigger difficulty calculation every 5 seconds.

* Add rxjs timer to difficultyEpoch.

* Fix pipe.

* Fix small bar position.

* Change i18n strings.

* Fix typo.

* Add time-until component.

* Speed up difficultyEpoch timer to 1000 ms.

* Fix values to 2 decimal places.

* Add title to fee and difficulty adjustment cards.

* Add title outside the card.

* Fix title to center position.

* Add other titles.

* Add new transalations strings.
Refactor time span component.

* Fix difficulty adjustment i18n string.
Fix duplicated i18n strings.

frontend/src/app/app.module.ts

@@ -32,7 +32,7 @@ import { FooterComponent } from './components/footer/footer.component';
 import { AudioService } from './services/audio.service';
 import { MempoolBlockComponent } from './components/mempool-block/mempool-block.component';
 import { FeeDistributionGraphComponent } from './components/fee-distribution-graph/fee-distribution-graph.component';
-import { TimespanComponent } from './components/timespan/timespan.component';
+import { TimeSpanComponent } from './components/time-span/time-span.component';
 import { SeoService } from './services/seo.service';
 import { MempoolGraphComponent } from './components/mempool-graph/mempool-graph.component';
 import { AssetComponent } from './components/asset/asset.component';
@@ -71,7 +71,7 @@ import { SponsorComponent } from './components/sponsor/sponsor.component';
     AmountComponent,
     LatestBlocksComponent,
     SearchFormComponent,
-    TimespanComponent,
+    TimeSpanComponent,
     AddressLabelsComponent,
     MempoolBlocksComponent,
     ChartistComponent,