Cannot export GIFs for multi-level gameplay

[ClementSparrow]

Currently, GIF export re-compiles the level to replay the recorded inputs, which means that only the gameplay of one level can be exported as GIF.

It also has the side effect that compiling is responsible for clearing the input history, which is not a responsibility that this function should have (especially since input recording should only exists in the editor and not in the engine, unless we add feature #35).