OpServiceTest: move to imagej.ops package
Move benchmarks to imagej.ops.benchmark

This is a simpler package name without the superfluous "tests" layer.
AbstractOpTest: move to imagej.ops package
OnTheFlyTest: move to imagej.ops.onthefly package

This rename also fixes a typo in the class name.
GaussTest: move to imagej.ops.convolve package
ConvolveTest: move to imagej.ops.convolve package
ConvertIITest: move to imagej.ops.convert package
AddConstantToNumericTypeTest: change the package

The class has moved to imagej.ops.arithmetic.add.
SlicerTest: move to imagej.ops.slicer package

This rename also singularizes the class name.
SlicingIterableIntervalTest: change the package

The class has moved to imagej.ops.slicer.

This rename also singularizes the class name.
ThreadedMapperTest: change the package

The class has moved to imagej.ops.map.parallel.

This rename also singularizes the class name.
SlicingIterableIntervalTest: use better assert

This way, if it fails, it will tell us what the expected and actual
values were.
SlicingIterableIntervalTest: simplify setUp
Merge branch 'unit-test-packages'

The SciJava convention is to put each test class in the same package as
the class it is testing. This also allows (if you wish) the ability to
test methods with protected and package visibility. It also makes the
src/test package hierarchy extremely straightforward, since it is 1-to-1
with the src/main package hierarchy.