Internal region with fixed displacement

Address #49

Example has internal region with fixed displacement. Both the x and y
boundary conditions are periodic. The example just displaces the
entire box at the moment.
Start ElasticFEModel

Address #49

Start of the ElasticFEModel class. The class generates a square grid
using Gmsh in a similar way to FiPy.

The prototype SfePy example ("elasticity/elasticiy.py") has been
compared with OOF and broadly agrees when comparing roughly for
displacement values in similar spatial locations. The SfePy example
has the wrong boundary conditions for the eventual problem that needs
to be solved
ElasticFEModel is nominally finished but broken

Address #49

ElasticFEModel is finished, but the first test run showed that the
file format is wrong for Sfepy. Will try and use the Sfepy's native
mesh classes to create the mesh.