UI: components facing camera should always face world position

If camera is added to another component so as to follow, facing
relative camera position will not work. This adds a helper to
calculate absolute camera position and use that to oriented gfx
UI: properly detect when multiple async resources are loaded

Previously if multiple resource id's were passed in as an array,
loaded callbacks would never be invoked as omega_id was being
checked on array.

Changes so that omega_id is checked on first array element
(all elements should have same omega_id)