No undo for cut & paste

Issue description

Build Plan is lost if the plan was cut [X] (not yet pasted) and the Game Screen is interrupted in any way, for example the battle screen. On returning back to the city, we see that the copied layout is forever lost. Only way of retrieving this is to use an old save file, if you r lucky.

Reproduction steps

1. Send the Cargo ship on the world map to a location where there is a possibility of a battle.
2. Design a small (or large) build keeping the Planning Mode ON.
3. As the Cargo ship is about to reach the destination, Press the X key to turn on the CUT mode.
4. Drag across the screen to cut the entire build and attach it to clipboard. Do not click on any other location to paste the layout yet.
5. Once the ship reaches the destination, the game is interrupted by the Battle screen.
6. Click on the back button on the Battle screen.
7. On returning back to the game, we see that the previously cut layout is forever lost. Only way of retrieving this is to use an old save file, that too, if you r lucky.

Game version and build number

Update 2 | v0.6.3 (b332)

Operating system

Windows