Function: Item.IO Both before Item.IO Input
Let Mappers extend Function
Consistent ordering of input/output in ThreadedMappers

First ItemIO.BOTH then ItemIO.Input (like in Functions)
Merge branch 'master' of https://github.com/imagej/imagej-ops
AddOp moved to "add" package
AddConstantToImageFunctional: Make it a function
AddConstantToNumericType: Added Priority
NeighborhoodOp: Make it a function
fixed parameter order

Item.BOTH first then Item.INPUT
Convolver: added final where possible
ConvertII: added final where possible
ConvertPix: Removed redundant in/out parameters
Gauss: Make it a function
ArithmeticOp: Changed parameter ordering

ItemIO.Both before ItemIO.Input
SlicingService: Changed parameter ordering

ItemIO.Both before ItemIO.Input
SlicingService: Added final where possible
ConvolveTest: Added final where possible
GaussTest: Added final where possible
InifityOp: Make it a function