(front) Improve show rating stars

A big simplification of the display of rating

dashboard/src/app/song-table/song-table.component.ts

@@ -1,4 +1,5 @@
 import { Component, EventEmitter, Input, Output } from '@angular/core';
+import { Utils } from '../utils';
 
 import { Song } from './../model/song';
 import { SortByPipe } from './../pipes/sort-by.pipe';
@@ -9,6 +10,7 @@ import { SortByPipe } from './../pipes/sort-by.pipe';
   styleUrls: ['./song-table.component.css']
 })
 export class SongTableComponent {
+  numberToArray = Utils.numberToArray;
   @Input() songs: Array<Song> = [];
   @Output() private atBottom = new EventEmitter();