GP framework only needs eigen3 now 

And also:
1) Fixed bug with wrong posterior Cholesky and alpha in exact inference method.
2) Added case test for ExactInferenceMethod, which checks partial derivatives of the negative marginal likelihood.
3) Replaced dynamic_cast with obtain_from_generic in methods of ExactInferenceMethod class.
4) Fixed printing of gradient result.
5) Integration test data updated.