Better interface for ResetMargin

The current interface of the ResetMargin is not symmetric in X and Y:

threshold.x is used to define the margin size for left and right sides
threshold.y.start is used to define the top margin size
threshold.y.end is used to define the bottom margin size (which is strange because "end" usually refer to an absolute coordinate in OTB world, not a margin size).

Also, the term threshold suggest an operation is performed based on the pixel value, which is not the case.

I propose to replace these parameters by 2 interfaces to set the region:

as a ROI, just like in ExtractROI:
- roi.startx
- roi.starty
- roi.sizex
- roi.sizey
as margins for each side
- margin.top
- margin.down
- margin.left
- margin.right

These parameters should be made consistent by the function ResetMargin::DoUpdateParameters().

To ensure API compatibility, it is possible to deprecate the threshold... parameters, while introducing the new ones roi... and margin....