This is a first full working version of an interface between EvtGen and
Sherpa's PHOTONS++ generator for final-state radiation.
This includes an additonal interface to use EvtGen's random-number generator inside Sherpa.
The intialisation of the interface updates Sherpa's KF_Table containing particle properties
based on EvtGen's PDL table.
The common model testing module was updated to add options for different FSR generators.
Also a few test files have been included to test different PHOTONS++ configurations.
The modifications required to link with Sherpa's libraries and to build sherpa from source
where included in the respective EvtGen compilation files.