Add an option to exclude files from the processing that do not have a TTree

In case of no events passing a given DSID and campaign, the output of TopCPToolkit is that no reco tree will be produced. This is annoting if there are multiple DSIDs being processed in one sample. We should add an option to skip those files automatically. Its an option and not the default since for this we need to open every single file and check if the TTree is there - this is potentially expensive e.g. with remote access.