Updated Polycode templates' Update() to add rendering
ATTENTION: ScreenEntityInstance no longer has a root entity, it is now loaded as children of the ScreenEntityInstance itself. You can now edit the default id, tags and custom properties of the entity itself. Entity tags will now check for duplicate before adding. Fixed numerous crashes relating to entity deletion in the 2d editor. Added a hasResource method to the ResourceManager.
Merge pull request #281 from TheCosmotect/master

Updated Polycode templates' Update() to add rendering
Added asset browser icons for entities and sprites
Made Resources remove themselves from ResourceManager in destructor. Should fix player crashing on quit