Hack together Sfepy linear elastic example

Address #49

Hack together Sfepy linear elastic example in order to seed the
MKS. Sfepy is easily installable, which allow us to use it as a
dependency. We want to generate the data during the test case
precluding the use of large FE tools for test cases.
Include position dependent material properties

Address #49

Position dependent material properties work. Question on Sfepy mailing
list addressed the problem.

https://groups.google.com/forum/#!topic/sfepy-devel/Zzzl1qz96zI
Include periodic boundary condition.

Address #49

The elasticity example does not work at the currently.
Periodic boundary conditions now work.

Address #49
Merge branch 'elasticity' of github.com:wd15/pymks
Resolve merge conflicts

Delete white space to resolve merge conflicts.