The enum GeometryType has been moved from grid.hh to here. That means that

there will be less dependence on the grid subdirectory.

Also, this file contains a new class NewGeometryType is should eventually
replace the old enum.  It is roughly as planned in FlySpray task 66.

The name NewGeometryType is obviously not satisfying.  I would have
prefered EntityType, ElementType, or GeometryType, but all of them
are taken already.

[[Imported from SVN: r3679]]