Bills initially working just as proof of concept

ng linted
modifier categories list is better at displaying data sanely now

bookie/src/app/sales/bills/bills-datasource.ts

@@ -0,0 +1,21 @@
+import { DataSource } from '@angular/cdk/collections';
+import { Observable } from 'rxjs';
+
+export class BillsDataSource extends DataSource<any> {
+
+  constructor(private data: Observable<any[]>
+  ) {
+    super();
+  }
+
+  connect(): Observable<any[]> {
+    return this.data;
+  }
+
+  /**
+   *  Called when the table is being destroyed. Use this function, to clean up
+   * any open connections or free any held resources that were set up during connect.
+   */
+  disconnect() {
+  }
+}