ENH : new parameter in writeFileITK to choose if Hfield or displacement

- add a boolean parameter to writeFileITK to choose if the Hfield needs to be converted to displacement field when dealing with writing a deformationfield
ENH : transform writeFileITK() into writeImageITK() and writeMapITK()

- Just like for applyMap where we separated the reader for a deformationfield and for an image, we do the same here
- We add the boolean parameter writeAsDisplacement to writeMapITK() which will indicate if we do or not the conversion with  HfieldToDeformationFieldFilter()
BUG : use writeImageITK() and writeMapITK() instead of writeImageITK() in applications and libraries

- for applications like GeometricMetamorphosis, LDDMM and MetamorphosisShooting, we added the boolean bWriteAsDisplacement that would be TRUE with the flag --writeAsDisplacement in the XML files, and used this value in writeMapITK()
- IMPORTANT : I don't really know how to set this boolean value (writeAsDisplacement) for the writeMapITK() in the librairies (objectiveFunctions, States, ImageManager and Algorithms) :
-- for the objectiveFunctions I assumed it should always be on false because this is inner processing within CalaTK
-- CStateInitialMomentum & CImageManager : No idea
-- CLongitudinalAtlasBuilder : I am wondering if it should not use a value set in the XML file of the Application "AtlasBuilder", and pass to this Algorithm
- IMPORTANT 2 : a LOT of writeFileITK have been replaced, errors could have occurred like using writeImageITK instead of writeMapITK or the other way around
- IMPORTANT 3 : the tests have not been updated for the replacement of writeFile