Modernize HltMonitors

• replace BOOST_FOREACH with range-based for loop
• replace boost/assign/list_of with (implicit) std::initializer_list
• do not implement derived methods that just call their base class version
• prefer STL algorithms over raw loops
• prefer implicit destructors
• remove obsolete SVN/CVS keywords
• prefer lambda callbacks over member function callbacks
• prefer .empty() over comparison with ""