ENH: Convert three ImageRegistration Examples to ITKv4

Here ImageRegistration examples 11 to 13, related to the optimizer
section of the ITKSoftwareGuide, are converted to use ITKv4 registration
framework for their registration processes.

Change-Id: Ib22f2cb06c2f7d811a05c982dfc3bf1f4e36c3e8
BUG: Use METER of sCAL scale unit

Change the scale unit field in the image to be PNG_SCALE_METER. The
image previously have a UNKNOWN unit type, which roduces a
warning in libpng 1.5, and the actual scale is ignored. This resulted
in the SignedMaurerDistanceMapImageFilterTest3 failure due to
different image spacings.

Change-Id: I3340f36fe1ce44308993f1720fc1fd2e66b88a2e
BUG: Use PNG_SCALE_METER for PNG sCAL unit

With libpng 1.5 if the unit is UNKNOWN when reading then an error is
printed, and the other spacing values are ignored. By writing METER
unit, the resulting png can be correctly read with spacing.

No unit conversion is done to preserve compatibility.

Change-Id: I74f4240221d31edecf2248425167659857326009
ENH: Add multi-Res and multistage registration Examples to ITKv4

MultiResImageRegsitration1 example is converted to use ITKv4 registration
framework along with the related explanations.

Also running a multistage regsitration process is completely
illustrated using two newly added examples to ITKv4.

Change-Id: I1301110a030e76b2c9d811de7303dbfc7c726b2d
Merge topic 'Exmpls11To13_standAlone'

6f2f4a39 ENH: Convert three ImageRegistration Examples to ITKv4
Merge topic 'PNGsCALSCALE'

29c0bfd2 BUG: Use PNG_SCALE_METER for PNG sCAL unit
16d252d8 BUG: Use METER of sCAL scale unit
Merge topic 'DefRegv4Expls'

166db74c ENH: Add multi-Res and multistage registration Examples to ITKv4