implement basic error handling and validation for forms

owrx/form/error.py

@@ -0,0 +1,15 @@
+class FormError(Exception):
+    def __init__(self, key, message):
+        super().__init__("Error processing form data for {}: {}".format(key, message))
+        self.key = key
+        self.message = message
+
+    def getKey(self):
+        return self.key
+
+    def getMessage(self):
+        return self.message
+
+
+class ValidationError(FormError):
+    pass