[BUGFIX] Fix and improve drag & drop of content elements

[webian]

• Add handle icon to start the drag of a CE
• Drag existing CE only from the handle icon to not interfere with the CE contents
• Display scroller also when user drags an existing CE from the website page
• Fix drop areas
• Hide drop zones that are childrens of the CE being moved because we don't want to drop a CE inside itself (e.g.: grid; container)
• Disable :hover of all CEs because when user starts to drag a CE the drop areas appear moving the CEs down so usually the previous CE is unintentionally hovered making its inline action toolbar and outline to appear and so creating confusion in the user

[webian]

fixed