Prefab Display modes

[ncannasse]

Talking with @trethaller regarding enabled/editorOnly - maybe we want to be able to set 3 bits per prefab:

• game : the prefab is make ingame
• preview : the prefab is make in hide (preview mode only)
• debug : the prefab is make in hide (debug mode only)
  All 3 bits can be set individually , enable=false is all bits set to 0
  And in hide we can switch between Preview/Debug render per prefab (default TBD) so we can have two display setup depending on usages.