Add MeshQuality class to help with quantifying mesh quality.

Includes support for making histograms for Matplotlib.
Add MeshQuality to tests.
Handle case that ratio = 1.0.

Pointed out by Chris Richardson.
Remove Armadillo unit test.
Unit test updates for mesh quality computattion.
More unit test fixes.
Merge branch 'garth/eigen'
Merge branch 'garth/mesh-quality-stats'