Modified getCoatBrownian()

Modified getCoatBrownian() to accept different Bulk and Shear Loss
Angles and calculate brownian noise using Hong et a. PRD 87, 082001
(2013).

New Function description:
This function calculates Coating ThermoOptic noise using
Hong et al . PRD 87, 082001 (2013).
All references to 'the paper', 'Eq' adn 'Sec' are to this paper.

***Important Note***
Inside this function phi is used for denoting the phase shift suffered
by light in one way propagation through a layer. This is in conflict
with present nomenclature everywhere else where it is used as loss
angle.

The layers are assumed to be alernating low-n high-n layers, with
low-n first.
Inputs:
         f = frequency vector in Hz
       ifo = parameter struct from IFOmodel.m
     wBeam = beam radius (at 1 / e^2 power)
      dOpt = the optical thickness, normalized by lambda, of each
             coating layer.
New required arguments:
       mTi = Mirror Transmittance
        Ic = Circulating Laser Power falling on the Mirror (W)
The following new arguments should be made available in the Materials
object and lines 108-110 and 116-118 should be uncommented:
 lossBlown = Coating Bulk Loss Angle of Low Refractive Index layer
 lossSlown = Coating Shear Loss Angle of Low Refractive Index layer
lossBhighn = Coating Bulk Loss Angle of High Refractive Index layer
lossShighn = Coating Shear Loss Angle of High Refractive Index layer
   PETlown = Relevant component of Photoelastic Tensor of High n layer*
  PEThighn = Relevant component of Photoelastic Tensor of Low n layer*
Returns:
SbrZ = Brownian noise spectra for one mirror in m^2 / Hz

*
Default values of PETlown and PEThighn are chosen from sec. A.1. to get
the longitudnal coefficent of photoelasticity as -0.5 as been asserted
by the paper there for Tantala and -0.27 for Silica.
These values also need to be added in Materials object.