Refs #9445. Added PeakFunctionIntegrator

PeakFunctionIntegrator takes an IPeakFunction and integrates it numerically using GSL routines.
Refs #9445. Fixed NaN-problem in PoldiTimeTransformer

PoldiTimeTransformer::detectorElementIntensity produced NaN when a
wavelength outside the spectrum boundaries was calculated, because that
would be negative.
Refs #9445. Added total intensity calculation to PoldiTimeTransformer
Refs #9445. PoldiCalculateSpectrum2D now integrates peak profiles