Refactored CMakeLists a little to place tests in subfolder.
Added simple ceres autodiff optimisation using Sophus unit test. Currently fails as std::abs and std::sqrt are not defined for jet types. ceres::abs and ceres::sqrt do exist. The best fix might be to alias the ceres functions into the std namespace, but this hardly seems good practice...
test_ceres: Replace magic constants with group defined values for clarity.
merge and fix ceres test (polishing needed)