Enable Drag Overlay

[arupargus]

The ngWidget structural directive should have config parameter enable_drag_overlay : <true|false> which enforces below behaviour

1. When we drag a widget .. it should not push the adjacent widget , but only overlay the active widget. until there is space to cascade the adjacent widget or the current widget in the cascade direction
2. . Horizontal drag will snap back to original position if the drag is released before enough space for adjacent widget swap to trigger
3. When we resize a widget .. it should push the adjacent widget in the resize direction