No easy way to remove filter cavity

There's no easy way to remove the filter cavity from budgets right now because the filter cavity loss needs to be manually removed. This will maybe be solved if sub-budgets are defined at runtime (#83) depending on how that's implemented. In particular, setting ifo.Squeezer.Type = 'Freq Independent' for the default A+ will calculate the quantum noise with frequency independent squeezing, but will fail because QuantumVacuumFilterCavity is hard-coded in the A+ init file. The proper way to do this is to define an ifo without QuantumVacuumFilterCavity, like aLIGO, but this is not obvious to a beginner. I'd love it if there was a way to inherit budgets instead of just ifo structs, but that's a long ways away.