ENH: ResampleImageFilter ReferenceImage only needs to match dimension

ResampleImageFilter can be supplied a ReferenceImage to use to define the
output spacing, origin, and directions. Previously, this ReferenceImage had to be
the same image type as the output.

Since only the meta-data is copied, the ReferenceImage only needs to be the
dimension as the output image.

This patch alters the prototype of SetReferenceImage()/GetReferenceImage()
to take/return pointers to an ImageBase instead of an output image type.

This change is useful, for instance, if you want to resample a labelmap
(image of labels) to match the domain of a VectorImage.

Change-Id: I52f4cb8617e72244a9d49299374dfef5333fcce6
BUG: Fixed while loop condition.

The while loop was counting on exceptions being thrown in order to terminate.
Here now we introduce a check for a normal condition of end of string.

Change-Id: I1851176812288bbb4d53443511031da80fe43ae0
ENH: Enable a VectorImage to be used as displacement field

Enable the WarpImageFilter to use a VectorImage type for the
displacement field.

It is not verified that the number of components matches the image
dimension.

The method used to obtain a displacement for a physical point, now
takes the output as an argument. This enables the output to be reused,
so that the VariableLengthVector would not have to be reallocated at
each pixel. It also reduce extra coping compared to returning by value.

Change-Id: I4825aff43992931acfd9a2d646cc8c937a151ceb
DOC: Update Migration guide schema URL

Also fix syntax error in LevelSetsv4VisualizationRename.xml.

Change-Id: I49497255af2c05047fb30d037bbaba2b6cd38814
Merge topic 'ResampleReferenceImage'

06d48ba ENH: ResampleImageFilter ReferenceImage only needs to match dimension
Merge topic 'MigrationGuideSchemaURL'

215df0f DOC: Update Migration guide schema URL
Merge topic 'WarpVectorImageDisplacementField'

ed241db ENH: Enable a VectorImage to be used as displacement field
Merge topic 'FixLogicInStringTools'

3563430 BUG: Fixed while loop condition.