Enable Simulation in XY mode using SPAM and collapse operators

[a-corni]

• SPAM errors are already implemented, but a bug needs to be fixed for simulation to be run with qutip.
• Everything is in place for the user to be able to perform simulations in XY using collapse operators.
  It does not make sense to develop other noise types since it uses microwave and if this is not implemented with a laser then:
• amplitude: no gaussian fluctuation in amplitude since since model works for a laser.
• doppler: speed will have an impact, but is it the same as for a laser ?
  A noise on the magnetic field might be more interesting ?
  @vdrouint @dehond