Add draggable scenery to Level Editor

[lauracumming]

Users currently have to click on any scenery elements to add them to their level creation. We would like users to be able to drag the objects across to the canvas.

The screen recording demonstrates that the users cannot currently drag the object and can only click on the object.

https://images.zenhubusercontent.com/18399425/ac56c190-fa77-4661-a910-57487337de85/non_draggable_demo.mov

https://www.codeforlife.education/rapidrouter/level_editor/#