Add FindNIFTICLIB.cmake module which only requires NIFTICLIB_DIR

[schuhschuh]

We should use a custom FindNIFTICLIB.cmake module (if necessary) to find the NIfTI library components which mainly asks the user for the installation directory of the library. The current module requires to specify the include directory and CDF, IO, and ZNZ libraries separately.

The FindNiftiCLib.cmake module of CMake BASIS could be used.

[schuhschuh]

As a side note, the code expects to find the NIfTI headers in the NIFTICLIB_INCLUDE_DIR directly, but my installation has them in <prefix>/include/nifti. The question is if it wouldn't be better to change the include statements to #include <nifti/nifti1_io.h>.

EDIT: This is BTW handled by my Find module, by simply adding both, the top-level include/ directory and the include/nifti/ directory.

# ----------------------------------------------------------------------------
# aliases / backwards compatibility
if (NiftiCLib_INCLUDE_DIR)
  set (NiftiCLib_INCLUDE_DIRS "${NiftiCLib_INCLUDE_DIR}")
  if (NOT NiftiCLib_INCLUDE_DIR MATCHES "/nifti/?$")
    list (APPEND NiftiCLib_INCLUDE_DIRS "${NiftiCLib_INCLUDE_DIR}/nifti")
  endif ()
  set (NiftiCLib_INCLUDES "${NiftiCLib_INCLUDE_DIRS}")
endif ()