Direct support for Abaqus mesh files in GridIn.

Direct support for Abaqus mesh files in GridIn.

The mesh_converter program is now considered obsolete and has been
removed from the contrib folder.
Direct support for Abaqus mesh files has been added to the GridIn
class through the function GridIn::read_abaqus(). An internal class
Abaqus_to_UCD captures all of the functionality of the original
mesh_converter program and feeds its output directly to the
already implemented GridIn::read_ucd() function. This is suboptimal
but works sufficiently well to act as an interim solution until the
internal renumbering scheme necessary to convert the Abaqus format
directly to deal.II's internal number can be determined.
On top of the already existing functionality to read in Abaqus meshes
created using Cubit, patches provided by Krzysztof Bzowski that allow
for the input of mesh files exported directly from Abaqus have also
been included.
Test cases have been added to the testsuite, with the original
mesh files from the mesh_converter program used for this purpose.