cleanups

[ms, c-c] new command checking for consistency / potentian flaws and enhancements of mapping file of a multi-sources instance

[repository] enabled sources refactoring: to avoid error, we should always have all known source in repo.sources_by_uri and only enabled ones in repo.sources, so we still have access to the definition of temporarily disabled sources

[migration] enhance RqlForIterator so we can do 'for e in rqliter(...).entities()'

[ms] when entity is coming from an external source, don't add non final relations on complete

[querier] add_types_restriction_cleanups: remove useless try/except (we already filtered out variables not in newroot.defined_vars) and dict accss. Also systematically set computed solutions instead of modifying existing ones