TrigNavigation+TrigDecisionTool: various const fixes
Various mostly trivial const-fixes to fix thread-checker warnings. The only user-facing interface change is to return a const reference instead of copy from TrigDecisionTool::getStreams().
Various mostly trivial const-fixes to fix thread-checker warnings. The only user-facing interface change is to return a const reference instead of copy from TrigDecisionTool::getStreams().