ENH: Move private constant and method to private header

Move the UpdateHeaderWithMinMaxMean method to the cxx file and move
the GenericUtilities header to the src directory as
itkMRCImageIOPrivate. The min_max_element method are kept private
this way. Additional style tweaks and header include reduction were
done.

Change-Id: I8ca007f87cac67b05e5554b656ff479c36a21255
STYLE: running uncrustify and manual fixups

Change-Id: I663acc21e8a09700300eb33ae8b7778e41b3e279
ENH: Moving MRCImageIO out of review

Removing line which registers ImageIOs for factories in side Review
module.

Change-Id: I2ccaf0602f00ce096299477960009babc2050ae5
Merge topic 'MRCImageIOOutReview'

c00935c ENH: Moving MRCImageIO out of review
134f8b2 STYLE: running uncrustify and manual fixups
6e491ae ENH: Move private constant and method to private header