BUG: Add ISC license header.
BUG: Add LICENSE file.
ENH: Add Spectra1DImageFilterTest skeleton.
ENH: Add Spectra1DSupportWindowImageFilter.
BUG: Update header file license headers.
STYLE: Remove deprecated ITK_EXPORT.
ENH: Spectra1DSupportWindowImageFilter class declaration.
STYLE: class TPixel -> typename TPixel.

Also fix some other whitespace issues.
ENH: Spectra1DSupportWindowImageFilter has a FFTSize.
ENH: Spectral1DSupportWindowImageFilter iterate through pixels.