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/sections/section-detail/section-detail.component.ts

@@ -1,5 +1,5 @@
 import { AfterViewInit, Component, ElementRef, OnInit, ViewChild } from '@angular/core';
-import { UntypedFormBuilder, UntypedFormGroup } from '@angular/forms';
+import { FormControl, FormGroup } from '@angular/forms';
 import { MatDialog } from '@angular/material/dialog';
 import { ActivatedRoute, Router } from '@angular/router';
 
@@ -15,20 +15,22 @@ import { SectionService } from '../section.service';
 })
 export class SectionDetailComponent implements OnInit, AfterViewInit {
   @ViewChild('nameElement', { static: true }) nameElement?: ElementRef;
-  form: UntypedFormGroup;
+  form: FormGroup<{
+    name: FormControl<string>;
+  }>;
+
   item: Section = new Section();
 
   constructor(
     private route: ActivatedRoute,
     private router: Router,
     private dialog: MatDialog,
-    private fb: UntypedFormBuilder,
     private toaster: ToasterService,
     private ser: SectionService,
   ) {
     // Create form
-    this.form = this.fb.group({
-      name: '',
+    this.form = new FormGroup({
+      name: new FormControl<string>('', { nonNullable: true }),
     });
   }
 
@@ -42,7 +44,7 @@ export class SectionDetailComponent implements OnInit, AfterViewInit {
   showItem(item: Section) {
     this.item = item;
     this.form.setValue({
-      name: this.item.name || '',
+      name: this.item.name ?? '',
     });
   }
 
@@ -93,7 +95,7 @@ export class SectionDetailComponent implements OnInit, AfterViewInit {
 
   getItem(): Section {
     const formModel = this.form.value;
-    this.item.name = formModel.name;
+    this.item.name = formModel.name ?? '';
     return this.item;
   }
 }