Improved hook to prevent multiple queries.
Merge pull request #184 from iamntz/class-hook

Improved hook to prevent multiple queries.
Small reorganisation of JS files & tweaks

- updated/added missing unminified vendors
- added grunt task runner
- removed a PHP notice if `NINJA_FORMS_JS_DEBUG` was already defined
- added a better way of defining backend class names
Added Fieldset form field

- Updated nestedSortable plugin
- SQL schema is updated to fit `parent` column
- fields are displayed in admin in a tree manner (also nesting fields is posible, althought it may not be such a great idea)
Optimised form-fields getter a little

- fixed form exports
Fixed form import
extra hook