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/regimes/regime-resolver.service.spec.ts

@@ -0,0 +1,15 @@
+import { inject, TestBed } from '@angular/core/testing';
+
+import { RegimeResolver } from './regime-resolver.service';
+
+describe('RegimeResolver', () => {
+  beforeEach(() => {
+    TestBed.configureTestingModule({
+      providers: [RegimeResolver],
+    });
+  });
+
+  it('should be created', inject([RegimeResolver], (service: RegimeResolver) => {
+    expect(service).toBeTruthy();
+  }));
+});