Help:$smwgCheckForRemnantEntities

Placeholder for #3866CiteRef::gh:smw:3866.

The impact (in terms of performance) on the updater is unknown since each update is expected to run additional queries therefore the setting is set on purge only by default.


 * `purge` enables the check to happen only during a purge action which limits a possible performance impact to a single subject request hereby avoids impacting regular updates
 * `true` as setting will carry out the check on every update
 * `false` will disable the check all together

@see #3849#issuecomment-477605049