Sales order support (#438)

* Add new models for SalesOrder

- Create generic Order and OrderLine models with common functionality

* Refactor

- Move some widgets around
- Cleanup directory structure

* Add link to home screen and nav drawer

* Add SalesOrder list widget

* Linting fixes

* Fix string

* Refactor PurchaseOrderDetailWidget

* Tweaks to existing code

* linting

* Fixes for drawer widget

* Add "detail" page for SalesOrder

* Add more tiles to SalesOrder detail

* Allow editing of salesorder

* add list filters for sales orders

* Display list of line items

* Customer updates

- Display customer icon on home screen
- Fetch sales orders for customer detail page

* Cleanup company detail view

* Create new sales order from list

* Stricter typing for formFields method

* Create new PurchaseOrder and SalesOrder from company deatil

* Status code updates

- Add function for name comparison
- Remove hard-coded values

* Update view permission checks for home widget

* Add ability to manually add SalesOrderLineItem

* Add nice progress bar widgets

* Display detail view for sales order line item

* edit SalesOrderLineItem

* Fix unused import

* Hide "shipped items" tab

- Will be added in a future update

lib/widget/progress.dart

@@ -2,6 +2,34 @@
 
 import "package:flutter/material.dart";
 import "package:flutter_overlay_loader/flutter_overlay_loader.dart";
+import "package:inventree/app_colors.dart";
+
+
+/*
+ * A simplified linear progress bar widget,
+ * with standardized color depiction
+ */
+Widget ProgressBar(
+  double value,
+{
+  double maximum = 1.0
+}) {
+
+  double v = 0;
+
+  if (value <= 0 || maximum <= 0) {
+    v = 0;
+  } else {
+    v = value / maximum;
+  }
+
+  return LinearProgressIndicator(
+    value: v,
+    backgroundColor: Colors.grey,
+    color: v >= 1 ? COLOR_SUCCESS : COLOR_WARNING,
+  );
+}
+
 
 /*
  * Construct a circular progress indicator