adding Ks->pipi->mumu monitoring

This adds an HLT1 line to monitor the Ks->pipi->mumu (i.e. double pi->mu misID) mass spectrum as an indicator of the muon efficiency when other channels are not available. Only tracks with p>10 GeV are selected to ensure four-fold coincidence is required by isMuon. Since there's an approximate probability of ~1.6e-4 of both pions from Ks->pipi to decay before reaching M2 (see plot), and given the abundance of Ks->pipi, part of the mass spectrum will be populated by real muons, although combinatorial hits can serve the purpose too.