POM: bump to pom-imglib2 5.1.1

This provides an improved enforcer configuration.
Changed fft dependency

Changed the fft dependency from jdk-mines to jtransform.
https://github.com/wendykierp/JTransforms

jdk-mines is still a testing scope dependency so that test comparing
jtransform and mines can be run.
Added NextSmoothNumber utility

A class to determine the next smooth number.  This is required so that
we can find the fast fft sizes.  Research and implemention performed by
Johannes Schindelin.

Based on A. Granville, Smooth numbers: computational number theory and
beyond.
FFTMethods: use more descriptive parameter name

Specifically, the complexToReal(RandomAccessibleInterval input,
RandomAccessibleInterval output, Interval interval, int dim,
boolean scale, ExecutorService service) method had its "interval"
parameter renamed to "unpaddedInterval".
Changed FFTMethods to use jtransform

FFTMethods was modified to use jtransform instead of Mines jdk.  Note
that JTransform performs fft using a packed format.

http://incanter.org/docs/parallelcolt/api/edu/emory/mathcs
/jtransforms/fft/FloatFFT_1D.html#complexForward%28float[]%29

The following functions had to be modified to call the JTransform FFT
instead of mines.

computeRealToComplex1dFFT
computeComplexToComplex1dFFT
computeComplexToReal1dFFT
JTransform vs Mines Tests

Added tests to verify that the jtransform version of FFTMethods and the
jdk-mines version produce equivalent results.
Add mines FFTMethods for tests