Created filters for loading fields and validation classes and added better handling of std values

1. Added filters to allow loading field and validation classes outside Redux folder structure, avoiding loosing custom field and validation definitions when updating the framework.
2. Added option 'std_show' to show std value when option not set, also to return std value in get() method. This change won't break current installations when updating since the new behavior must be explicitly turned on.
3. Added option 'std_mark' to show a mark by the fields title when the value is not set and it is showing the std value, by default this option is set as an empty string to keep with current behavior.