Merge branch 'bugfix/6449_fixMDBoxSplittingPerformance' of https://github.com/mantidproject/mantid into Branch_bugfix/6449_fixMDBoxSplittingPerformance
refs #6449 fully hide BoxControllerWithBoxTracking

(will remove bunch of warnings)
Merge branch 'bugfix/6449_fixMDBoxSplittingPerformance' into develop