Allow output ROOT files to be browsed from the web app

JSROOT is promising for this: https://jsroot.gsi.de/latest/?file=https://root.cern/js/files/hsimple.root&item=hpx

The output file from this pipeline is probably a good starting point: https://lhcb-analysis-productions.web.cern.ch/1161972/LbToL0ll/2017_MagDown_LEPTONIC/