Build with libinsighttoolkit4-dev only on amd64 and i386

Insighttoolkit4 package is not build on different architectures
123
Restore dependency on libfftw3-dev

This is necessary when building with libinsighttoolkit3-dev, due to this
bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=740628
Refresh nd-backport.patch
Release to unstable