Add ir.message and use custom exceptions

issue3672

exceptions.py

@@ -0,0 +1,19 @@
+# This file is part of Tryton.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+from trytond.exceptions import UserError, UserWarning
+
+
+class ImportStatementError(UserError):
+    pass
+
+
+class StatementValidateError(UserError):
+    pass
+
+
+class StatementValidateWarning(UserWarning):
+    pass
+
+
+class StatementPostError(UserError):
+    pass