aacenc: Refactor the parts of the AAC psymodel.

3GPP:
Remove ffac from and move min_snr out of AacPsyBand.
Rearrange AacPsyCoeffs to make it easier to implement energy spreading.
Rename the band[] array to bands[]
Copy energies and thresholds at the end of analysis.

LAME:
Use a loop instead of an if chain in LAME windowing.
