NEW : adding CheckIfNewHeader in ApplyMap

- the method is going to compare the source image and the sourceToTargetMap
- the Map has one more dimension holding the deformation vectors, but this dimension is written after the space dimensions. Therefore, when checking the header, it's going to compare the good first dimensions and stop before the deformation field.
BUG : allowing small relative differences ( < 1.0e-6) for inputs spacing

- when using LDDMM, we encountered a difference between the spacing of the Map computed and the spacing of the source image ( 0.019999999552965164 instead of 0.02). This allows to use CheckIfSameHeader in applyMap if the difference is small enough.