adding lowest unprescaled single tau triggers to LS2_v1 menu

Antonio De Mariarequested to merge
single_tau_trigger_LS2 into master

Adding lowest unprescaled single tau triggers to the LS2_V1 menù. Reference page:

https://twiki.cern.ch/twiki/bin/view/Atlas/LowestUnprescaled

Tagging @carquin and @malconad

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