Update to Demo - Fixes

Some fixes in this update for common issues that have become apparent as the demo has had a wider audience.

• Fix: stored and player-made creatures have their neurological DNA overwritten on birth
  
• Fix: stored and player-made creatures pass the wrong DNA on to their children, resulting in extreme maladaption over time
  
• Fix: when you spawn a stored creature, it immediately splits into multiple 'species' even though they all descend from the same originator
  
• Allow modified creatures to mutate physiologically after enough generations have passed
  
• Fix: bug that could result in player-made creatures being culled upon maturation
  
• Fix: some issues with removing plants
  
• Allow changing brush size when removing plants
  
• Fix: plankton don't reproduce correctly if it's the first thing placed
  
• Fix: eggs, seeds and plankton sometimes phase through cave walls and ceilings