core: expose `is_source` on `MovementHistoryListBrain`
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.