add general strain response function and move ifo_power to lib.py

* add the function strain_response to lib.py which calculates the
general strain response. The Strain calibration in noises.py now uses
this function evaluated at an azimuthal angle of 15 deg to reproduce
the old calculation
* move ifo_power to lib.py and use that instead of
optimize_PRM_transmissivity
3 jobs for !139 with access_optimization in 1 minute and 45 seconds (queued for 5 seconds)
latest merge request