Extend LookAtController to allow 'upAxis' to be defined.

LookAtController (and by implication HoverController) assumes that up is in the +Y direction. The purpose of this pull request is to allow the up direction to be set by the user of these classes.
Merge pull request #576 from ChrisDenham/patch-1

Extend LookAtController to allow 'upAxis' to be defined.