fft2.FFT: restore expecting scaling behavior when calling to FFTMethods

Noticed by Stephan Preibisch:
The recent changes I introduced to the class, aimed at making it
prossible to control the number of threads used for computation,
introduced some mistakes related to the expected scaling of the results.

When using FFTMethods calls in the FFT class, the scaling must be as
following:
- calls to complexToComplex(): if forward=true then scaling=false
  if forward=false then scaling=true.
- complexToReal(): scaling is always true.
- realToComplex(): scaling is always false.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
added corresponding methods that do not require to specify the number of threads
For some reason this fails to compile on jenkins, reverting it

Revert "added corresponding methods that do not require to specify the number of threads"

This reverts commit 23c1fc20ace5e1f091f0117c1458c86d4259742b.
Revert reversion

The Jenkins failure was due to the ImageJ Nexus service being down.

I brought it back online, and all should be well now.

Revert "For some reason this fails to compile on jenkins, reverting it"

This reverts commit ce27291ce50eb888c2606916daebcfed56e329ad.
Merge branch 'master' into knip