Head Center Offset + Optitrack Plugin

this should allow to track a user in front of the screen without changing the view position, so tunneling data, e.g., from OptiTrack that was read through an OptiTrack plugin on to the VA Plugin.

Also allows HeadToCenter offsets.

assigned to @jonathan.ehret

changed the description

added 4 commits

• 1f7f5636...100a4951 - 2 commits from branch 4.26
• 335acf1e - Merge remote-tracking branch 'origin/HEAD' into feature/headcenter_tracking
• 384f4745 - cleanup code and add some more comments

Compare with previous version

mentioned in commit 3fd97dce

merged