fix in muon low energy options
The loading of the special MuonLowEnergy.xml to reset the cuts in the filter requires at the moment a postConfigAction. While this has been fixed with a work around in AppConfig (lhcb-datapkg/AppConfig!141 (merged)) it should also be fixed here.
Note that in the restructuring of the Gauss() configurable we should find a better way to handle this.