Menu editor improvements

User Stories:
As a CMS user I want to be able to edit existing hst:parameternames / hst:parametervalues in the ChannelManager.
As a CMS user when I create a new SitemenuItem and a prototype has been defined ( see HSTTWO-3438 ) then the parameters of the prototype are added to the new sitemenuitem.
As discussed with Stephan Westen the word "Parameters" should omitted from the dialog.
As discussed with Adrian Collier and Arthur Bogaart a scrollbar should be displayed if the parameters don't fit anymore in the dialog.
As discussed with Adrian Collier a layout where the inputbox in located under the label, similar to the "title" field, is Ok