Explicit construction of fixedPointSet with 0 PointData from reference mesh.

Before this change, it was assumed that there is a 0 scalar field defined on the reference mesh. With this change we remove this requirement and explicitly construct a new fixedPointSet from the reference mesh. We add the 0 scalar field explicitly. This example should now work with any shape model.
Bugfix: alignment of deformation fields fixed.

The alignment was done using a resample image filter, which does a
coordinate transform of the deformation fields.
This is not the correct behavior. Instead, the coordinate system should
stay the same, but the deformation field has to be manipulated to deform
the reference to a data set of different alignment.
Merge branch 'fix_lmconstraint_model_builder' of https://github.com/marcelluethi/statismo into marcelluethi-fix_lmconstraint_model_builder
Bugfix: Removed the PosteriorModelBuilder3DTest

That test had a hard-coded path to a local 3D shape model. Instead, the
test functionality has been added to the PosteriorModelBuilderTest.
Merge pull request #35 from tom-albrecht/ModelBuilderTestBugFix

Bugfix: Removed the PosteriorModelBuilder3DTest