widgets editor date/date-time handling improvements

Use momentjs to replace extjs date-time parsing and provide support for more ISO date-time formats (see http://momentjs.com/docs/#/parsing/string-formats/) in gco:DateTime

Allow gco:Date (handled by extjs DateField) to have yyyy-mm-dd, yyyy-mm and yyyy granularity and maintain that granularity in editor sessions

(Retry of previous pull request which got munged)