Miscellaneous features

At my project I needed more flexibility in rendering forms, but I did not want to create separate templates for each case. I added set of features which should allow easier styling without changing templates. Changes includes:

- new options for validate() function 'noSetError' to not add error messages to the screen when validating form/field
- automatically generate classes for wrapper element
- allow to specify field prefix and suffix HTML
- for 'Radios' field editor add 'selected' class to wrapping <li> of selected radio button
- Tests for these new features
- Updated documentation