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-340 ) then the parameters of the prototype are added to the new sitemenuitem.

As discussed with swesten the word "Parameters" should omitted from the dialog.

As discussed with acollier and abogaart a scrollbar should be displayed if the parameters don't fit anymore in the dialog.

As discussed with acollier a layout where the inputbox in located under the label, similar to the "title" field, is Ok