Validate relation existences and counts independently from heatup

[kaikoga]

Background

MotionSet must have an initMotion set in seeds, but don't want to check it through heatup API

Note: Instantiating from code with null values or explicitly setting null from code should be overlooked

Barriers had problems (they required the object to be warm API, which was bad for some use cases, and also barriers could not check object existence in collections)

Implementation

• Through seed structure
  • Could be checked on load
  • Cannot detect implicit references, which makes this plan useless
• Through verify method
  • Should be more robust
  • When?
  • I think we should make sure all Externals have finished populating objects before starting heatup anything (currently achieved through barriers)

[kaikoga]

Maybe break @:arpBarrier and do @:arpBarrier(NonNull, Warm) ?