Fix default field type in forms (#645)

Fixes #628. Minor fix providing a valid default for the form field type.

coderedcms/forms.py

@@ -186,7 +186,7 @@ class CoderedFormField(AbstractFormField):
         max_length=16,
         choices=FORM_FIELD_CHOICES,
         blank=False,
-        default="Single line text",
+        default="singleline",
     )