Improve artefact drag

- Fix memory issues for BoardArtefact objects (Currently cheking placement of all artefacts 60 times a second when dragging an artefact. 
- Moving Artefacts should be restricted to the board only (Currently possible to move around all over the board, and out of page
- Position is fixed so placement stays even if window is minimized etc)  	
- Bring Dragged artefact to the top of z axis