BUG: Fixes #179 broken unit tests caused by tests not having classes for...

Fixes FieldEditorTest, UserDefinedFormTest and UserDefinedFormControllerTest which was caused by the tests not having classed defined for ExtendedEditableFormField which is specified in the Yaml fixture file.
Removed it from the fixture file and created a new fixture file for EditableFormFieldTest which does use ExtendedEditableFormField