[Checkbox] add tagName prop

[giladgray]

• add tagName prop so you can have a checkbox not wrapped in a <label>, which causes event problems when you listen for click on a parent element.
  • obnoxious DOM side effect: pretty sure this is because clicking a label around an input also clicks the input and ends up triggering a whole bunch of events.
  • set tagName="div" to render a beautiful checkbox that can be clicked directly (but not the text)