Center HMD HUD and magnifiers on default eye position
Fix similar problem for HMD third person view

getUprightHeadPosition() changes with avatar lean.
Remove unused methods
Fix some build warnings while in the vicinity
Minor adjustment to Oculus pick ray calc
Merge pull request #3735 from ctrlaltdavid/20126

CR for Job #20126 - Rift HUD shouldn't move with head