GRIFFIN Ancillary detector efficiencies

[AdamGarnsworthy]

We need to include some information on DESCANT efficiency of this page. I have asked Paul and Vinzenz if any efficiency curve exists or if we have some efficiency value for all energies.

If DESCANT is mounted then only 4 LaBr3 can be present. We need to add the option for this in a similar manor as it is done for HPGe.