Starrating now inherits from delite/FormValueWidget, and uses separate DOMNodes for left and right half of stars

Implements enhancements requested in https://github.com/ibm-js/deliteful/issues/145 and https://github.com/ibm-js/deliteful/issues/1
seems dojo/string is required only for substitute() calls. Would it be possible to use String.replace() instead ?