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/home/home.component.html

@@ -173,6 +173,14 @@
   >
     <h3 class="item-name">Taxes</h3>
   </mat-card>
+  <mat-card
+    class="flex flex-col square-button mr-5, mb-5"
+    matRipple
+    *ngIf="auth.allowed('regimes')"
+    [routerLink]="['/', 'regimes']"
+  >
+    <h3 class="item-name">Regimes</h3>
+  </mat-card>
   <mat-card
     class="flex flex-col square-button mr-5, mb-5"
     matRipple