CMS-3916 Live Edit - After refactoring it is no longer possible to manually move the context menu

- added moveBy method for contextMenu
- added drag listeners to itemView contextMenu
- also added click listeners to context and tab menus to prevent click through on menu itself
Merge pull request #871 from enonic/cms-3916

CMS-3916 Live Edit - After refactoring it is no longer possible to manua...