Time merge

Bring all of time travel into master!

Things that work:
Going back in time for all divergent entities.
Forking from the point back in time and generate a new divergent entity.
A simple time visualization.


Things left for time travel:
Delete entities when timeline is finished.
Detect forks in alternate timelines
Fix collsion with two divergent entities: i.e. if bottom entity jumps and you stand on top it locks up
Non divergent back time travel (where you don't spawn a new entity, you just redo what you did)


Play around with it and let me know if I broke anything. Make an issue if so.