BUG: Fix Cppcheck build with ninja.

Cppcheck only builds with make.
ENH: SegmentTubeSeeds logic fixed.
Merge pull request #316 from thewtex/cppcheck-ninja

BUG: Fix Cppcheck build with ninja.
Merge pull request #317 from aylward/ComputeSegmentTubeParams

ENH: SegmentTubeSeeds logic fixed.
COMP: Adding test tolerance to deal with 32bit and other machine diffs
Merge pull request #318 from aylward/TextTolerance

COMP: Adding test tolerance to deal with 32bit and other machine diffs
COMP: Increasing test tolerance for machine variations
COMP: Relaxing tolerance requirements
Merge pull request #319 from aylward/TextTolerance

Text tolerance
COMP: Fix warnings on signed/unsigned comparison
Merge pull request #320 from aylward/DashboardWarningsSignedComp

COMP: Fix warnings on signed/unsigned comparison
BUG: RidgeExtractor set xstep to 3-vector regardless of image dim
Merge pull request #321 from aylward/RidgeExtractorDimensionalityBug

BUG: RidgeExtractor set xstep to 3-vector regardless of image dim
Fix Convert TRE xml and readme
Improve spatial object node support

The vtkMRMLSpatialObjectNode used to only support VesselTubeSpatialObjects
which can be a problem as the files from Convert TRE can be only
TubeSpatialObjects (VesselTubeSpatialObject's superclass).
This commit allow the vtkMRMLSpatialObjectNode to support loading
TubeSpatialObject.
Also replace static_cast by dynamic_cast.