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/api.dart

@@ -650,16 +650,20 @@ class InvenTreeAPI {
    * e.g. "part", "change"
    */
   bool checkPermission(String role, String permission) {
+
     // If we do not have enough information, assume permission is allowed
     if (roles.isEmpty) {
+      debug("checkPermission - no roles defined!");
       return true;
     }
 
     if (!roles.containsKey(role)) {
+      debug("checkPermission - role '$role' not found!");
       return true;
     }
 
     if (roles[role] == null) {
+      debug("checkPermission - role '$role' is null!");
       return true;
     }