Avoid creation of temporary object when creating SpatiallyVaryingKernel. Fixes #124.
fix the following warning

statismo/modules/VTK/examples/vtkSpatiallyVaryingGPModelExample.cxx:93:25: warning: expression result unused [-Wunused-value]
        centerOfMass[d] * V;
Merge pull request #126 from statismo/issue_124

Fix #124 on develop