Regard column mapping for elements as constant

Also revert to using a hard-coded boost::iterator; the run-length
iterator will return as a separate class later.
Map between fine and coarse grid

Helper object that does the upscaling part between the fine grid and
the coarse top surface.
Upscaling of rock and fluid properties

Volume-weigthed average of porosity and permeability. Viscosity and
density stay the same.
Update example to use upscaled fluid objects
Move all files into module directory

Even though we plan to submit some of the files to the core project
later, it is probably confusing if they are in its namespace but
located physically here.
Access run-length encoded zig-zag matrices

These wrappers enable you to write code that accesses the run-length
encoded matrices in UnstructuredGrid and the like without having to
worry about the indirect accessing of the position matrix.