Support for boost::intrusive::set

[johanst]

I have added visualizers for boost::intrusive::set and and associated iterator. There are four flavors: base_hook default member_hook default base_hook / constant_time_size member_hook / constant_time_size

I tried to add visualizers for intrusive lists with constant_time_size but the visualizer code does not seem to support it.

[KindDragon]

Thank you!