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
Move unimportant prerequisites inside functions and classes where used.

Move unimportant prerequisites such as Fipy, pyFFTW, etc. into the function and classes where they are used. User can import pymks without an error now.

Fix #56
Merge branch 'elasticity' of github.com:wd15/pymks
Resolve merge conflicts

Delete white space to resolve merge conflicts.
Revert "Rename `_test` to `test`"

This reverts commit e424a093760ce62360081d08f9765239cd494ddb.

The 'elasticity' branch was unintentionally merged into the master branch. Revert back to branch before merge.
Resolve conflicts in master branch.

Resolve minor conflicts between the master branch and the
learningCurves branch.
Resolve minor conflicts with master
Remove elastic directory for master branch.

Unintentionally merged elastic branch with master. Removing directory to fix.
Merge branch 'master' into learningCurves

Conflicts:
	pymks/fipyCHModel.py
Add learning curves and edit notebook `04 - Cross Validation`

Edit notebook `04 - Cross Validation`. Remove exercises from seminar and provide examples for users to mimic. Add learning curves.