ENH: noise models - added A, B, C, and D weightings to SPL

The SPL can now be weighted according to the new 'SPLweighting' entry
that can be set to:
- none: no weighting
- dBA : dB(A)
- dBB : dB(B)
- dBC : dB(C)
- dBD : dB(D)

This commit also includes code refactoring of the  noiseModel class to
remove the dependency on noiseFFT/declutter.