Use boost::bimap

[Dade916]

Use boost::bimap instead of 2 hast tables, sets, etc. in all definition repositories inside Scene class.

[Dade916]

boost::bimap, like standard map, uses a tree to keep items sorted (instead of an hash table). So it is slower than boost::unordered_map and it is not the right solution.

[Dade916]

My previous post is not entirely correct, it is just the default behavior. boost::bimaps::unordered_set_of can be used to have hash maps.

[Dade916]

Done.