CDB-2951 threaded some heavy user-related rakes
CDB-2951 more threaded + some style cleaning
Merge branch 'master' into CDB-2951

Conflicts:
	lib/tasks/db_maintenance.rake
CDB-2951 Merged with master improvement. Not mem-safe approach but faster and server should be able to cope with it
Merge branch 'master' into CDB-2951
CDB-2951 submodule update (to grab keeping whenever possible updated_at, created_at and cartodb_id) + test rake
Merge pull request #484 from CartoDB/CDB-2951