Find Eigen on Macs configured with Boxen.
Download Eigen into the build dir if it is not found on the system.
Use Eigen 3.1.4.
Merge pull request #223 from bilke/ExternalProjectEigen

Configure Eigen as an external project (if not installed)
Removed debug output.
add FemEnums.h
add ShapeMatrices
add NaturalCoordinatesMapping
include Eigen in Tests if OGS_USE_EIGEN
add TestShapeMatrices
add TestCoordinatesMapping
[NL] Move ShapeMatrixType into ShapeMatrices.h
[NL] Add missing iostream include.
[NL] Uncrustify.
[NL] Improve constness in NaturalCoordinatesMapping.
[TNL] ShapeMatrices: Use isZero/isOnes in tests.

Replace ASSERT with EXPECT.
add missing tests for ShapeMatrixType::DNDR and DNDR_J
improve readability of NumLibFemNaturalCoordinatesMappingQuad4Test
use isZero() and isOnes(), and divide CheckFieldSpecification to smaller pieces