Fixed problem with surface space and stereotaxic space annotations...

Fixed problem with surface space and stereotaxic space annotations disappearing (going behind) a flat surface when the surface view zooming value is less than one.  The solution is to disable depth testing when drawing an annotation in surface/stereotaxic space on a flat surface.

An alternative that also fixed the problem is when scaling the view of a flat surface, always use a value of one for scaling in Z in BrainOpenGLFixedPipeline::applyViewingTransformations().  This solution might affect the ‘3D’ view of some shapes.