Agree on scheme for intergration over frequency bands

[eacharles]

The OG BoloCalc code has a couple of different things that it down in terms of defining frequency bands.

1. It computes frequency dependent quantities at a number of frequency points, as specified by either the channel BANDS file, or the channel bandwidth, and the frequency resolution parameter.
2. It defines a top-hat window function using the 3dB roll-off points on either edge of the band, and uses this for any computations that involve quoting efficiencies.
3. All integration over bands is done with trapezoid rule integration.

Right now I'm mixing these two up a bit, but only computing frequency dependent quantities inside the band as defined by the 3dB windows. This will give identical results for efficiencies, but slightly smaller results for powers.

We should agree on how to do this.