Level editor and arcade mode

This update contain some candy for the creative mind.

The highlights are: - Support to create arcade levels in the built-in level editor. - Support to share your levels with other players and play levels they have created.

Extra: - Added a restart level button to speed up exploration and avoid tedious/repetitive undo clicking. - Added support for using the backspace key to undo a move. - Fixed a zoom in/out bug that made the camera flip 180 degrees. - Fixed issue where a block could fall even though Max did not touch the block.

Here is a video showing how you can create a level and share it with the world:

https://www.youtube.com/watch?v=X9qdYJBC3Ds

Please note that there are more features than shown in the video but this video aims to cover the basics.

A shout-out to Dohi64 for a lot of great input about things to improve. This update does not cover everything mentioned but it should be a step in the right direction.