Update handler_url support to match the latest in the xblock repo, for both js and python runtimes

[LMS-1613]

common/static/coffee/src/xblock/runtime.v1.coffee

@@ -4,9 +4,21 @@
     childMap[child.name] = child
 
   return {
-    handlerUrl: (handlerName) ->
+    # Generate the handler url for the specified handler.
+    #
+    # element is the html element containing the xblock requesting the url
+    # handlerName is the name of the handler
+    # suffix is the optional url suffix to include in the handler url
+    # query is an optional query-string (note, this should not include a preceding ? or &)
+    handlerUrl: (element, handlerName, suffix, query) ->
       handlerPrefix = $(element).data("handler-prefix")
-      "#{handlerPrefix}/#{handlerName}"
+      suffix = if suffix? then "/#{suffix}" else ''
+      query = if query? then "?#{query}" else ''
+      "#{handlerPrefix}/#{handlerName}#{suffix}#{query}"
+
+    # A list of xblock children of this element
     children: children
+
+    # A map of name -> child for the xblock children of this element
     childMap: childMap
   }