Update: blobs, decaying sawblades, enhancements

What's new:

• The NPC enemies are now blobs instead of the buglike creatures, sometimes they stop and change their direction as well.
• Sawblades are destroyed automatically after 3 kills.
• It is now impossible to place objects on top of players.
• There are some performance stats at the top (current FPS, CPU and GPU usage); it will be hidden by default later.
• Bugfix: it was possible to destroy objects that were not placed yet.