Add NODATA support to changematrix operator

[Damianofds]

In order to port the changematrix operator in the master branch a NODATA support must be introduced.

Objectives

• Allow the user to specify different NODATA ranges for the reference and actual images
• Write a NODATA on the output image when in the pixel value change is involved a NODATA
• store in the mappings results the transitions with a NODATA involved. use as NODATA value the minimum value allowed by the type of the output matrix

Actions

• Add in the ParameterBlock 2 new input values of type Range which represents the NODATA range for the reference and the actual image. If one (or both) of them are null (or an empty range) means that there aren't NODATA values in that image
• for each internal loop, after the pixel comparation is perform, check if the values belong to their related NODATA range, if yes add the result to the proper transition

Example

Reference Image has a NODATA range: all values <= 0 Actual Image has a NODATA range: value = 0 OutputImage has type Short

Reference[i] = -3; Actual[i] = 6 Result: OutputImage[i] = NODATA; changematrix.registerPair(-32768,6) //-32768 = Short.MIN_VALUE

[Damianofds]

Clarification The NoData range must be the same for both reference and actual images. Since we want to compute the changes between the two images that are produced with the same process (but, f.e. they repèresent the same area in 2 different time) 2 different NODATA doesn't make sense.