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/regimes.module.spec.ts

@@ -0,0 +1,13 @@
+import { RegimesModule } from './regimes.module';
+
+describe('RegimesModule', () => {
+  let regimesModule: RegimesModule;
+
+  beforeEach(() => {
+    regimesModule = new RegimesModule();
+  });
+
+  it('should create an instance', () => {
+    expect(regimesModule).toBeTruthy();
+  });
+});