• remove placeholder when dragging widget below grid (already worked when dragging left, above, and to the right of grid).
• prevent extra checks for removing widget when dragging off grid.
• trigger added when a widget is added via dropping from one grid to another.
• trigger removed when a widget is removed via dropping from one grid to another.
• trigger removed when a widget is removed via dropping on a removable zone (#607 and [#550])(#550)).
• trigger custom event for resizestop called gsresizestop (#577 and #398).
• prevent dragging/resizing in oneColumnMode (#593).
• add oneColumnModeClass option to grid.
• remove 768px CSS styles, moved to grid-stack-one-column-mode class.
• add max-width override on grid-stck-one-column-mode (#462).
• add internal functionisNodeChangedPosition, minor optimization to move/drag.
• drag'n'drop plugin system. Move jQuery UI dependencies to separate plugin file.