[feature-merge] When importing a grid, display an area that needs to be cleared instead of using FindFreePlace

[Jimmacle]

If the grid is dynamic, the whole area needs to be cleared of all objects. If the grid is static, the whole area needs to be cleared of grids and floating objects.

This will allow grids to be imported in their original location, making it easier to replace stations and otherwise cumbersome objects where it's easier to move everything else out of the way.