[rset] cubes such as iliane hi-jack rset description by poping some lines from it. Handle this on RepeatList

[undo] basic support for undoing of entity creation / relation addition

[undo] init entity cache when undoing an entity deletion

[undo] consistent is/is_instance_of processing

[repo] don't need rset description on those queries

[cleanup] style fixes, add nodes, 0.2 cents refactorings

[undo] during undoing, call hooks in the [active]integrity and undo categories

[repo] refactor fti operation to use set_operation and a single operation whatever the number of entities to ft index

[querier] introduce RepeatList class, used to optimize size of data returned for result set description When rql query has no ambiguity, we used to return the same description * N where N is the size of the result set. Returning RepeatList class avoid that multiplication. According to quick benchmark this improve performance for result set whose size is ~ > 50, has very small penalty for rset < 50, and in any case improve the size of data to be transfered over the network through pyro connection.

[repo] on add entity, set cache as soon as possible + fill type/source cache