More precise schema failure message

While creating schema for the add-on I used, I realized that my error
message was not precise enough.

For a big configuration such as in "Enhance main window", the message
"None is not of type 'string'" is almost useless.
So I added a path in the json config, to indicate where the error
is. And also which subschema is currently being used.

qt/aqt/addons.py

@@ -1330,7 +1330,14 @@ class ConfigEditor(QDialog):
         except ValidationError as e:
             # The user did edit the configuration and entered a value
             # which can not be interpreted.
-            showInfo(tr(TR.ADDONS_CONFIG_VALIDATION_ERROR, problem=e.message))
+            showInfo(
+                tr(
+                    TR.ADDONS_CONFIG_VALIDATION_ERROR,
+                    problem=e.message,
+                    path="/".join(str(path) for path in e.path),
+                    schema=str(e.schema),
+                )
+            )
             return
         except Exception as e:
             showInfo(_("Invalid configuration: ") + repr(e))

qt/ftl/addons.ftl

@@ -6,4 +6,4 @@ addons-failed-to-load =
     {$traceback}
 # Shown in the add-on configuration screen (Tools>Add-ons>Config), in the title bar
 addons-config-window-title = Configure '{$name}'
-addons-config-validation-error = There was a problem with the provided configuration: {$problem}
+addons-config-validation-error = There was a problem with the provided configuration: {$problem}, at path {$path}, against schema {$schema}.