Feature: Tax Regimes are added so that different bills with different series can be printed for Different regimes such as VAT and GST

Chore: Model relationships updated to make them simpler
Chore: Bill printing majorly refactored for it

Due to the sheer depth of the changes. There can be showstoppers. Please test it carefully

bookie/src/app/sales/bills/bills.component.html

@@ -46,7 +46,7 @@
           ><button>Table: {{ bs.bill.table.name }}</button> /
           <button mat-button (click)="choosePax()">{{ bs.bill.pax }} Pax</button> /
           <button mat-button (click)="chooseCustomer()">
-            {{ bs.bill.customer?.name || 'Customer' }}
+            {{ bs.bill.customer?.name ?? 'Customer' }}
           </button></mat-header-cell
         >
       </ng-container>