Fix rotate in ortho mode
Fix rotate in ortho mode

The centre of rotation for the mouse rotation interaction was set with
reference to the window origin, which led to odd behaviour when rotating
in ortho mode for the top two panels. The origin is now set with
reference to the current Projection.

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3