This can be useful when making a report on movements and when we list properties of the movements that depend on the side but are not directly exposed on MovementHistoryListBrain. One use case was Movement_getSpecificReference, which shows source_reference when the brain is for the source and destination_reference otherwise.

With this new approach, instead of guessing we record the "is_source" information at indexing time, when we know this for sure.

This also simplifies MovementHistoryListBrain.date and MovementHistoryListBrain.mirror_date which no longer need to guess the side and fix a problem that because this guessing was done using movement.getSourceUid() - which cause security errors when users can not access the source of the movement.