Product Group renamed to Menu Category

Extracted Product Group -> Group_type to a a new object called Sale Category.
Moved tax from product to Sale Category for uniform taxes on types of sales.

bookie/src/app/home/home.component.html

@@ -10,8 +10,11 @@
 <a mat-raised-button  routerLink="/tables">
   Tables
 </a>
-<a mat-raised-button  routerLink="/product-groups">
-  Product Groups
+<a mat-raised-button  routerLink="/menu-categories">
+  Menu Categories
+</a>
+<a mat-raised-button  routerLink="/sale-categories">
+  Sale Categories
 </a>
 <a mat-raised-button  routerLink="/products">
   Products