Added set_header functions to prepare in BaseHandler
Added set_header functions to prepare in BaseHandler

cannin/tmpnb,marscher/tmpnb,parente/tmpnb,cannin/tmpnb,marscher/tmpnb,marscher/tmpnb,parente/tmpnb,parente/tmpnb,willjharmer/tmpnb,cannin/tmpnb,jupyter/tmpnb,ianabc/tmpnb,ianabc/tmpnb,willjharmer/tmpnb,parente/tmpnb,marscher/tmpnb,jupyter/tmpnb,ianabc/tmpnb,willjharmer/tmpnb,jupyter/tmpnb,ianabc/tmpnb,cannin/tmpnb,jupyter/tmpnb