Swap orddict for dict in orswot and map

After a report on IRC of Maps with 13k set elements inside taking up to 80seconds to merge, I ran some benchmarks comparing `dict` and orddict` (as I had a suspicion this was the bulk of problem.)

This PR swaps orddict for dict. There may well be many more optimisations to do, but as the attached graph, and tables below show, this is a mighty big speed up.

{TODO, add the graph and tables when I get to my other machine}