Resolve "OPAL-FEL (MITHRA integration)" with stub class option
Refers to #535 (closed) This MR is a copy of MR 440, only that in this case the OPAL_FEL feature is enable through a "stub class" approach
Refers to #535 (closed) This MR is a copy of MR 440, only that in this case the OPAL_FEL feature is enable through a "stub class" approach