Code style check in form field list

I have changed FOFFormFieldList:: for self:: since is a local static member reference.
Merge pull request #43 from javigomez/fix_code_style_in_fof_form_field_list

Code style check in form field list
Merge branch 'development' of https://github.com/akeeba/fof into development

# By Javier
# Via Javier (1) and Nicholas K. Dionysopoulos (1)
* 'development' of https://github.com/akeeba/fof:
  Code style check in form field list