Make notes widget "generic" (#327)

* Make notes widget "generic"

- No longer tied to the "part" model
- Will allow us to use it elsewhere

* Update release notes

* Add helper methods for checking model permissions

* Refactoring of permissions checks

* Add notes to the "purchase order" widget

* Fix typos

* remove bom tab from part view

* linting fixes

lib/inventree/model.dart

@@ -10,6 +10,7 @@ import "package:inventree/api.dart";
 import "package:inventree/api_form.dart";
 import "package:inventree/fa_icon_mapping.dart";
 import "package:inventree/l10.dart";
+import "package:inventree/helpers.dart";
 import "package:inventree/inventree/sentry.dart";
 import "package:inventree/widget/dialogs.dart";
 
@@ -78,7 +79,63 @@ class InvenTreeModel {
     } else {
       return "";
     }
+  }
 
+  /* Return a list of roles which may be required for this model
+   * If multiple roles are required, *any* role which passes the check is sufficient
+   */
+  List<String> get rolesRequired {
+    // Default implementation should not be called
+    debug("rolesRequired() not implemented for model ${URL} - returning empty list");
+    return [];
+  }
+
+  // Test if the user can "edit" this model
+  bool get canEdit {
+    for (String role in rolesRequired) {
+      if (InvenTreeAPI().checkPermission(role, "change")) {
+        return true;
+      }
+    }
+
+    // Fallback
+    return false;
+  }
+
+  // Test if the user can "create" this model
+  bool get canCreate {
+    for (String role in rolesRequired) {
+      if (InvenTreeAPI().checkPermission(role, "add")) {
+        return true;
+      }
+    }
+
+    // Fallback
+    return false;
+  }
+
+  // Test if the user can "delete" this model
+  bool get canDelete {
+    for (String role in rolesRequired) {
+      if (InvenTreeAPI().checkPermission(role, "delete")) {
+        return true;
+      }
+    }
+
+    // Fallback
+    return false;
+  }
+
+  // Test if the user can "view" this model
+  bool get canView {
+    for (String role in rolesRequired) {
+      if (InvenTreeAPI().checkPermission(role, "view")) {
+        return true;
+      }
+    }
+
+    // Fallback
+    return false;
   }
 
   // Fields for editing / creating this model