first commit of a working calypso to start EDM

First barebone project for Calypso based on Athena 21.0. Only packages necessary to implement the current EDM in xAOD are included. The current build relies on Gaudi and AthenaExternals libraries. This should be okay for FASER, as we don’t want or need to build these two on our own. It currently also uses some of the ATLAS scripts to set environment variables – these can be replaced with either the spelled-out commands or our own scripts in the future.