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/taxes/tax-detail/tax-detail.component.html

@@ -18,6 +18,16 @@
           <span matSuffix>%</span>
         </mat-form-field>
       </div>
+      <div class="flex flex-row justify-around content-start items-start">
+        <mat-form-field class="flex-auto">
+          <mat-label>Regime</mat-label>
+          <mat-select formControlName="regime">
+            <mat-option *ngFor="let reg of regimes" [value]="reg.id">
+              {{ reg.name }}
+            </mat-option>
+          </mat-select>
+        </mat-form-field>
+      </div>
     </form>
   </mat-card-content>
   <mat-card-actions>