COMP: Fix and improve ForwardFFTExample

The failing test is fixed by padding the input image to the right size.
Update calls were removed where not needed, to use the pipeline.
The write update calls were put in try/catch blocks as usual.
I added more tests, so that all the outputs are tested.
I enhanced the documentation by adding screenshots from the resulting images.

Change-Id: I363d5cdc0fb9d259aaa5ff52cddbaaeb412c32b4
Merge "COMP: Fix and improve ForwardFFTExample"