TrigCost: enable thread-checker and fixes

Enable the thread-checker for all "TrigCost" packages and apply the necessary fixes:

• EnhancedBiasWeigher:
  • Use Gaudi::Accumulators for calculating averages in an atomic way.
  • Derive ReadLumiBlock from cool::Application to avoid static.
• RatesAnalysis:
  • Derive RateHistoBase from AthMessaging to ensure we use thread-safe logging. Has the additional benefit that we can now use the usual ATH_MSG macros for logging.
• TrigCostAnalysis
  • const and cmake fixes

cc @aporeba