Add charts to currency page

src/app/currency/currency-history.model.ts

+import { Moment } from 'moment/moment';
+
+export class CurrencyHistory {
+  constructor(membersCount?: number, blockNumber?: number, timestamp?: Date, monetaryMass?: number) {
+    this.membersCount = membersCount;
+    this.blockNumber = blockNumber;
+    this.timestamp = timestamp;
+    this.monetaryMass = monetaryMass;
+  }
+
+  membersCount: number;
+  blockNumber: number;
+  timestamp: Date;
+  monetaryMass: number;
+}
+
+export interface CurrencyHistoryFilter {
+  before?: Moment;
+  after?: Moment;
+}
+
+export class ChartMembers {
+  constructor(dataPoints: DataChart[], label: string) {
+    this.dataPoints = dataPoints;
+    this.label = label;
+  }
+  type: string;
+  dataPoints: DataChart[];
+  label: string;
+}
+
+export class DataChart {
+  constructor(x: string, y: string) {
+    this.x = x;
+    this.y = y;
+  }
+
+  x: string;
+  y: string;
+}