use jQuery by default
update ThumbImageFileInput
take off dropZone ( gen from js instead), and make exif as feature
inputWrapper should contains image-cover and input widget
document html structure
set data-exif on fileInput element
use Div class instead of Element class,

It should render both open tag and close tag.
should not in single tag with empty elements
ThumbImageFileInput update

Add formkit-widget-thumbimagefile class to inputWraper
simply enable exif option
extract cascading attriute class methods to Element class.
add underscore prefix to _supportedAttributes
prepend underscore prefix to attribute member
remove CascadingAttribute class
remove CascadingAttribute from dependnecy
set _customAttributes to protected
rename addAttribute to registerCustomAttributes
update method docs
rename $standardAttributes to $_standardAttributes
should be protected
set $children member as protected and renamed to _children