Added shader type as a property of the mapper.

This can be used to change shader modes between direct volume rendering
(DVR), MIP and MIDA.
Add ways of adjusting render types for the fixed and moving volume data.

Standard DVR, MIP and MIDA are now implemented. Default is DVR.
Removed apple related stuff.
Added support in the mapper for switching between shader types for fixed and moving volumes.
Added another mapper that uses custom shaders with the same functionality as the multi volume render.

Supports DVR, MIP and MIDA.