topicmap: massive rework
Massively rework the way we build and use topicmap. This bring massive performance
benefit.
Topic map use to be a fully independant thing that we would switch on and off
globaly. The caching on disk was broken so the performance were atrocious.
Intead, now the topic are inherited from the 'immutable' map. We gave up on
storing them on disk for now since the mutable set is usually small enough.
The activation is done by hacking new "filter" on the repository and detection
when they are one. This is hacky but core is hard to wrap here.
Overall this whole wrapping is really scary and we should massage core API to
help it.