Extra interface to Geant4 UserAction classes

Added extra interface level between RunManager and UserActions. This will allow to use the same UserActions in sequential and multi-threaded modes.

EM physics of the production physics List QGSP_FTFP_BERT_EML was updated to be the same as in Geant4 10.0, the only different - multiple scattering for electrons below 100 MeV is unchanged.

This modification should not be merged to 7_1_X so far.