New colormaps and removed a log in vtkvmtkBoundaryLayerGenerator

Added new colormaps in vmtkcenterlineviewer, vmtkmeshviewer, vmtkpathlineanimator and vmtksurfaceviewer: cooltowarm (default), rainbow, blackbody and grayscale. Added the possibility to set NumberOfColors (default 256). Removed the grayscale flag (0,1).
Removed a log (tangle triangles found) from vtkvmtkBoundaryLayerGenerator.cxx