By default interp beams to UVData freqs

[steven-murray]

Almost always the input UVBeam will need to be interpolated to the input UVData frequencies before simulation (it's hard to imagine a case where you wouldn't). Some simulators MAY have ways to do this inside the simulator, so we don't necessarily always want to do it in the ModelData class, but we should do it by default and allow turning that behavior off with a parameter.