add error messages when saving/deleting features fails

Saving and deleting of features is now stopped when any failure occurs. Functions return QgsFeature or None, or bool indicating
if operation was succesfull. Database throws still an error message also, but should throw only one.

Author: nmaarnio

arho_feature_template/core/models.py

@@ -562,8 +562,8 @@ def from_config_data(cls, data: dict) -> PlanFeature:
         # TODO: Implement
         return cls(**data)
 
-    def describe(self) -> str:
-        return f"{self.name} " if self.name else ""
+    def __str__(self):
+        return self.name if self.name else ""
 
 
 @dataclass