Merge branch 'master', remote-tracking branch 'upstream/master'
first version of dataset templates (compiles for trivialVectorialRepresenter)
changed all vtk examples to new representer structure (compiles, but not thoroughly tested)
changed itk examples to new representer structure.
Merge remote-tracking branch 'origin/dataset_templates' into dataset_templates
Merged standard represents and adapted it to new representer structure.

This commit successfully compiles, but the code is still largly untested.
Moved representer traits using in StandardImageRepresenter to separate file.
Introduced Preprocessor class.

Changed swig wrapping to new structure and made all tests compile.
All test pass. ITK and VTK examples compile with new representers.
Introduced new ModelBuilder for building models specified by an arbitry Gaussian process.
Made Dimensionality of MatrixValued Kernels a constructor argument (used to be a template parameter)
added itk wrapping for LowRankGPModelBuilder
New examples that shows how deformationmodels can be created using the Gaussian Process approach.
BugFix: CloneDataset did delete the clone before returning it
Moved all but the standard representers to a new folder deprecated.
Removed all references to the old representers from the examples.
fixed typo in UncorrelatedMatrixValuedKernel
Changed statismo::VOID  to statismo::Void, to avoid problems on windows.

Windows defines #define VOID void, which causes compilation problems with above expression on windows.
Added support for VTK 6.
removed unnecessary typename qualifier
Fully advanced hybrid image to image registration program.
Simple Gaussian process image to image registration program.