ENH: RSS module - Add rejection label

Before this commit, the RSS module works as: given a seed label image, the surface grows from the seeded region and grab the target region.
But in case of leakage, it is not able to prevent such leakage by assigning some rejection region.

This commit introduced the possibility of rejection label. There is no added parameter. Just in the input label image, use another color(label) to mark the rejection region.

say we draw a seed label image using two colors/labels: 1 and 2, 10, 24. Then the contour will grow from label 1 (label of interest, default is 1 and can be adjusted)
and moreover it will NOT grow into label 2/10/24.
STYLE: Rss module - Clean up code

Remove comment code
Remove files from txx to hxx
Remove omp preprocessor because this introduce racing condition.
ENH: RSS module - Post processing output mask

During level set evolution, the sub-0-level-set will not grow into the rejection region. However, during thresholding level set function,
with a > 0 threshold, the original rejction label region may be assigned as "in target" which is not desired.
this post processing further use input label image to avoid such a situation
PERF: RSS module - Only post process when needed

Only post-process the label map when we see more than one labels in the input label image
STYLE: RSS module - change variable name

change bUseRejctionLabelImage to useRejectionLabelImage
STYLE: RSS module - Add Marc Niethammer to contributor

The first version of rejection label was done by Marc. Thanks Marc!
STYLE: RSS module - merge confliction

Merge branch '3475-add-rejection-label-to-rss-module' of github.com:gaoyi/Slicer into 3475-add-rejection-label-to-rss-module

Conflicts:
	Modules/CLI/RobustStatisticsSegmenter/RobustStatisticsSegmenter.cxx