Quantum noise sub-budgets

1. Adds quantum noise sub-budgets. This addresses 1/3 of #51 (closed). Quantum noise can now be broken up into

• AS port vacuum
• Arm loss
• SEC loss
• Filter cavity loss
• Injection loss
• Readout loss
• Quantum quadrature phase noise

2. Changes the quadrature phase noise calculation as described in the comments below. This should close #20 (closed).
3. Removes support for negative RMS phase fluctuations.
4. Removes call to shotrad4 in some cases since this function no longer exists.

The sub-budgets are only implemented for the Cosmic Explorer interferometers since these are the only ones that have any other sub-budgets. Adding sub-budgets to the other interferometers is easy. The CE2 quantum budget is shown below as an example.

gwinc/ifo/noises.py

@@ -148,8 +148,7 @@ def precomp_suspension(f, ifo):
 def precomp_quantum(f, ifo):
     pc = Struct()
     mirror_mass = mirror_struct(ifo, 'ETM').MirrorMass
-    pbs, parm, _, _, _ = ifo_power(ifo)
-    power = Struct(parm=parm, pbs=pbs)
+    power = ifo_power(ifo)
     noise_dict = noise.quantum.shotrad(f, ifo, mirror_mass, power)
     pc.ASvac = noise_dict['ASvac']
     pc.SEC = noise_dict['SEC']