Bugfix: Added check to avoid segmentation fault, when no vtk files are
found.
Added Statistical Model Kernel and made Kernels dependent on representers.

The class StatisticalModelKernel was added to the list of supported kernels.
This change required the use of PointType (instead of VectorType) for the kernel evaluations. Hence the Kernels need to depend on the representer.
Merge pull request #23 from marcelluethi/statistical_model_kernel

Added StatisticalModelKernel