Sokoban + Level editor (0.2)

This update contains the following changes and improvements:

• Ability to launch and play a level directly from the editor.
• Update to some of the GUI elements (Cleaner icons and better scaling).
• Update to some of the premade levels (The levels are the same, but they are now better distributed).

This is just a quick prototype and I don't expect to invest a lot of time on it, but I still want to polish some things and have a "clean" little game and editor.