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 ""