Patch 0.8.4.174

This patch has a number of bug fixes and stability improvements for the Track Editor

• Added a 'Play' tab to the Editor. This tab will have more settings and options when 0.8.5 comes out later this month such as 'Play Reversed' and 'Test Single Race / Time Trial/ Survival' etc...
  
• Fixed a crash where nodes could become null during multiple undo-redo's.
  
• Fixed a crash where Editor Entities could become null during a Track Editor session.
  
• Fixed a crash where Water size doesn't deserialize properly. Default sizes added as a fallback.