Multi-select objects

When you need to move/delete/replace more than one item, you can now make one action for all instead of making separate actions for each object!

How it works:
When the user holds SHIFT and starts dragging on the empty space on the
map, they will see a selection polygon. With this polygon the user can select
multiple objects.

Multi-selected objects will be highlighted and the user will see a widget with the
preview of all selected objects.

On the multi-select widget, the users can remove all objects in one go, remove
them by category (all objects of the same category will be removed) and swap
by category (all objects within the category will be changed to the new selected
object).

When dragging one of the highlighted objects, all the selected objects will move
(the cursor style changes and the popup message on the bottom left appears).

Moving with keyboard arrow keys works for multi-selected objects works the
same way as when selecting a single object. After selecting an object/objects
you can move them by pressing arrow keys on your keyboard.

All the selected objects can be copied or moved to the other floorplans. In the
''Placed objects" menu, there is a sub-menu ''Multiple objects actions'' where
you can choose to Copy or to Move selected object/objects to the new
floorplan.

Hidden objects and folders are not available for selection, also if the user
selects an object and then hides it, this object will be excluded from selection
and will disappear from the selected objects widget.