For backward compatibility, we import the migrated enums to the dune.common
namespace.

This patch exports all enum-types defined in dune-grid (or added by
dune-python and associated to dune-grid) to the Python namespace
dune.grid.

Due to the changes in dune.grid, the PartitionIteratorType is no longer
required and, hence, is removed. It has been superseeded by the exported
partition objects.

also only add plot/triangulation method to 2d grids

x[:] now returns the underlying numpy buffer and x[1:3] the slice
not that x is itself not a numpy array, so for transpose one needs
x[:].transpose() to get the transposed view of the field vector.

The same works for entity(x)[:] but also now
localpoints = numpy.array([lx1,lx2,lx3,lx4],[ly1,ly2,ly3,ly4]]
coords = entity(numpy.array(localpoints)
coords[0] = numpy.array([gx1,gx2,gx3,gx4])
with (gx1,gy)=entity.geometry.position((lx1,ly1))
coords[:] = numpy.array([[gx1,gx2,gx3,gx4],[gy1,gy2,gy3,gy4]])
etc.

Note that the global coordinates are computed when coords[] is called so only
calling coords.local[] does not lead to overhead

GCC 7.2.0 is otherwise unhappy about using `rows` as a template
parameter.

Closes: #28

add 'dune-py' to end of the cache directory name

See merge request staging/dune-corepy!30

(cherry picked from commit 010edd8fa4e68884bbf7b9f68f8db1a8f02481d6)

now users get base/dune-py/dune-py instead of (as before) base/dune-py.

that an exception is raised instead of a bool returned

the new configuration check possibilities

removes them in case HAVE_ALBERTA or HAVE_DUNE_UGGRID is not set in dune-py/config.h

dunecontrol also uses `DUNE_BUILDDIR`.

directory via the DUNE_PY_DIR environment variable. This avoids bad things
happening when a user just uses $HOME instead of $HOME/dune-py